RECOMMENDATIONS FOR ADJUSTING WEIGHTS FOR ZAMBIA POST-HARVEST SURVEY DATA SERIES AND IMPROVING ESTIMATION METHODOLOGY FOR FUTURE SURVEYS

Transcription

1 FOOD SECURITY RESEARCH PROJECT RECOENDATIONS FOR ADJUSTING WEIGHTS FOR ZABIA POST-HARVEST SURVEY DATA SERIES AND IPROVING ESTIATION ETHODOLOGY FOR FUTURE SURVEYS By David J. egill WORKING PAPER No. 13 FOOD SECURITY RESEARCH PROJECT LUSAKA, ZABIA arc 2005 (Downloadable at: ttp:// )

2 ACKNOWLEDGENTS Te Food Security Researc Project is a collaboration between te Agricultural Consultative Forum (ACF), te inistry of Agriculture, Food and Fiseries (AFF), and icgan State University s Department of Agricultural Economics (SU). We wis to acknowledge te financial and substantive support of te United States Agency for International Development (USAID) in Lusaka. Researc support from te Global Bureau, Office Agriculture and Food Security, and te Africa Bureau, Office of Sustainable Development at USAID/Wasngton also made it possible for SU researcers to contribute to ts work. Comments and questions sould be directed to te In-Country Coordinator, Food Security Researc Project, 86 Provident Street, Fairview, Lusaka; tel: ; fax: ; fsrp@coppernet.zm ii

3 FOOD SECURITY RESEARCH PROJECT TEA EBERS Te Zambia FSRP field researc team is comprised of Jones Govere, Billy wiinga, Jan Nijoff and Ballard Zulu. SU-based researcers in te Food Security Researc Project are Antony Capoto, Cynta Donovan, Tom Jayne, David Tscrley, and icael Weber. iii

4 TABLE OF CONTENTS Acknowledgments... ii Food Security Researc Project Team embers... iii Table of Contents... iv 1. Background Review of te Total Number of Rural Agricultural Houseolds from te PHS Weigted Data Series Review of PHS Sampling, Listing and Weigting Procedures Review of 1990 and 2000 Zambia Census Data on te Total Number of Rural and Urban Houseolds and Agricultural Houseolds Recommended PHS Weigt Adjustment Procedures Preliminary PHS Weigt Adjustment Options Based on te Projected Number of Rural Houseolds Proposed odified Weigt Adjustment Procedure Based on Projected Number of Rural Agricultural Houseolds etodology for Estimating Projected Number of Rural Agricultural Houseolds Based on 1990 and 2000 Census Data Possible Refinements of Adjusted PHS Weigts Review of te Percentage of Agricultural Houseolds in PHS Frame Weigts for te 2004 PHS Supplemental Panel Survey Recommended Canges in te Listing and Weigting Procedures for Future PHS and CFS Consideration for Special Crop Weigts Annex 1. Tables for Review of PHS Weigting etodology...19 iv

5 Recommendations for Adjusting Weigts for Zambia Post-Harvest Survey Data Series and Improving Estimation etodology for Future Surveys 1. BACKGROUND Te Central Statistical Office (CSO) as been conducting te Zambia Post-Harvest Survey (PHS) annually for about 15 years. Ts survey is one of te most important sources of data in Zambia for te annual production of crops and livestock, as well as socio-economic caracteristics of agricultural ouseolds. In reviewing te results from te annual series of PHS results, it was found tat tere as been considerable variability in te total number of rural agricultural ouseolds over time, wit noticeable jumps in years were tere was a cange in sampling metodology. Since ts affects te estimates of total crop and livestock production, te CSO and te Food Security Researc Project (FPRP) decided to review te survey sampling and weigting metodology tat as been used for te PHS in te past. Based on te findings from ts review, a weigt adjustment procedure is proposed to provide more consistent annual PHS estimates for ts data series. Te purpose of ts report is to document te findings from ts review of te PHS sampling, listing and estimation metodology and te proposed weigt adjustment procedures, as well as to make recommendations for improving te metodology for te PHS and Crop Forecasting Survey (CFS) in te future. ost of te tables in ts report are included in Annex I, given te size of te tables, but tey are an integral part of ts report. In reviewing te PHS sampling, listing and weigting metodology, te consultant ad valuable input from te CSO staff, including. Sooka, Director of te Agricultural Division, Colby S. Nyasulu, Senior Statistical Officer, and Solomon Tembo, Systems Analyst. Valuable insigts were also provided by odesto Banda, CSO Deputy Director, and Julius Sawa, inistry of Agriculture and Cooperatives (ACO) Deputy Director, in a meeting to discuss te best strategy for improving te PHS and CFS metodology. Trougout te visit te consultant worked in close consultation wit Jan Nijoff and Jones Govere of te Food Security Researc Project (FSRP) of icgan State University (SU), wit remote consulting from argaret and Donald Beaver of SU. 1

6 2. REVIEW OF THE TOTAL NUBER OF RURAL AGRICULTURAL HOUSEHOLDS FRO THE PHS WEIGHTED DATA SERIES In order to understand te need for ts review of te PHS metodology and te nature of te proposed weigt adjustment procedures, we sould begin by examining te distribution of te weigted total number of agricultural ouseolds from te annual PHS data series starting wit te 1990/91 survey. Table 1 of Annex I sows te estimates of total number of agricultural ouseolds by district for eac PHS based on te original survey weigts. It can be seen in Table 1 tat at te national level te weigted total number of agricultural ouseolds varies considerably by year, wit significant jumps in te PHS series for te years 1991/92, 1995/96 and 1999/2000. Tese particular years correspond to major canges in te PHS sampling metodology. For example, in 1995/96 a new sample was introduced based on te selection of te census supervisory areas (CSAs) and standard enumeration areas (SEAs) wit probability proportional to size (PPS); and beginning wit te 1999/2000 PHS only agricultural ouseolds were included in te last stage sampling frame from te listing. Te purpose of te weigt adjustment procedures will be to provide more consistent annual PHS estimates of te total number of agricultural ouseolds and related survey estimates. 2

7 3. REVIEW OF PHS SAPLING, LISTING AND WEIGHTING PROCEDURES Prior to te new sample design for te 2002/03 PHS (documented in te report on Recommendations on Sample Design for 2003 Zambia Post-Harvest Survey Based on New Sampling Frame from te 2000 Census, egill, November 2003), te PHS sample ad been based on te 1990 Census frame. A stratified tree-stage sample design was used for te PHS. Te stratification of te sampling frame was originally based on te 53 old districts, but ts was later canged to te 68 new districts. Te primary sampling units (PSUs) were te CSAs, selected wit probability proportional to size (PPS) witn eac stratum. At te second stage one SEA was generally selected witn eac sample CSA, also wit PPS; a few CSAs ave more tan one SEA selected. A new listing was conducted witn eac sample SEA, and ouseolds were selected at te trd sampling stage witn two farm size categories (A and B). In reviewing te previous PHS sampling frame based on te 1990 Census, one finding was tat te number of ouseolds in eac CSA and SEA used for te PPS selection was different from te corresponding number of ouseolds in te 1990 Census data. Apparently a precensus cartograpc frame ad been used for te PHS instead of te final 1990 Census count of ouseolds. A review of te measures of te size for te CSAs in one district indicated tat te number of ouseolds in te CSA was generally ger in te PHS pre-census sampling frame tan in te 1990 Census data. As long as te number of ouseolds in te PHS sampling frame is gly correlated wit te corresponding number from te 1990 Census, ts sould not ave a major effect on te efficiency of te sample design. Anoter finding was tat in some districts tere are sligt differences between te CSAs and SEAs classified as rural in te 1990 Census, and te corresponding areas in te PHS sampling frame. Some CSAs and SEAs classified as urban in te 1990 Census are included in te PHS sampling frame, and a few areas considered rural in te 1990 Census are excluded from te PHS frame. Table 2 of Annex I sows te total number of rural ouseolds by district from te 1990 Census, and te corresponding census figures for te number of ouseolds in te CSAs and SEAs included in te PHS frame, as well as te difference between tese two. Discussions wit CSO staff indicated tat in some cases like Cngola District, some rural areas were incorrectly coded as urban in te 1990 Census results. In oter cases, suc as Kabwe Urban District, te CSO staff included some urban CSAs in te PHS frame because tese areas ad rural caracteristics. A few rural CSAs were excluded from te PHS frame because tey ad refugee camps. For te PHS series prior to 1999/2000, te non-agricultural ouseolds were included in te frame for size category A in te listing for eac sample SEA, but ten te metodology was canged to include only agricultural ouseolds in te last stage sampling frame. Te issue of te percent of agricultural ouseolds in te rural areas is addressed in Section 7. Also, te non-contact ouseolds (for wc te enumerator was not able to obtain information) are being excluded from te last stage sampling frame, resulting in a downward bias in te survey estimates of totals. Anoter concern regarding te listing is tat sometimes te number of ouseolds listed in a sample SEA is not consistent wit te corresponding count from te census frame, or wit previous listing results. Any undercoverage of te listed ouseolds will also result in a downward bias in te survey estimates of totals. Recommendations for improving te listing and estimation procedures are presented in Section 9. 3

8 4. REVIEW OF 1990 AND 2000 ZABIA CENSUS DATA ON THE TOTAL NUBER OF RURAL AND URBAN HOUSEHOLDS AND AGRICULTURAL HOUSEHOLDS In studying te weigt adjustment procedures for te PHS data series, it is important to examine te distribution of te number rural ouseolds from te 1990 and 2000 Censuses witn eac of te old districts, sown in Table 2. Ts table also sows te total number of rural agricultural ouseolds from te two censuses for eac district and te corresponding percent of agricultural ouseolds. One reason for using te old districts for ts comparison is tat it was easier to obtain te summary data from eac census for tese districts, since te new districts were formed by subdividing some of te old districts. It can be seen in Table 2 tat te growt rate for rural ouseolds varies considerably by district; in a couple of districts te number of rural ouseolds actually decreased sligtly during ts 10 year interval. In te case of Cngola District, te extremely g increase in te number of rural ouseolds is actually related to te possible miscoding of some rural areas as urban in te 1990 Census data. Te growt rate of te rural ouseolds by district will be used in te weigt adjustment procedures, as described in te next section. 4

9 5. RECOENDED PHS WEIGHT ADJUSTENT PROCEDURES Initially two alternative weigt adjustment procedures were considered for te PHS data series. Bot of tese metods are discussed ere to examine wc model would be te most appropriate for adjusting te weigts. Te conditions under wc eac alternative adjustment procedure would be appropriate are also discussed. Ten te recommended adjustment procedure is specified, wc is a modification of one of te preliminary alternatives Preliminary PHS Weigt Adjustment Options Based on te Projected Number of Rural Houseolds Te preliminary PHS weigt adjustment alternatives tat were examined are based on te projected total number of rural ouseolds eac year in a particular district, assuming an exponential growt rate calculated from te 1990 and 2000 Census data. Te main reason for using te total number of rural ouseolds for te projections is tat data on agricultural ouseolds from te 1990 and 2000 Censuses do not appear to be consistent. It can be seen in Table 2 tat te overall percentage of rural ouseolds wit agricultural operations from te 1990 Census data was 58.1 percent, compared to te corresponding 2000 Census estimate of 87.9 percent. Altoug it is possible tat te actual percent of agricultural ouseolds in te rural areas increased sligtly during ts 10-year interval, te implied growt rate from tese two census estimates appears to be too extreme. It is possible tat te data on agricultural ouseolds from te two censuses are inconsistent because of te different forms and data collection metodology used for eac census. As indicated in te next section, te 2000 Census appears to be a more accurate source of data for agricultural ouseolds. Te preliminary alternative weigt adjustment procedures described ere rely on te PHS data to determine te percentage of agricultural ouseolds in eac sample SEA, available in te survey data up to te 98/99 PHS. Initially it was tougt tat te listing information could be used for te PHS weigt adjustment procedures, but it was found tat te listing seets for te earlier PHS years are lost, and information on non-agricultural ouseolds is not available in te listing information starting wit te 1999/2000 PHS. Te first alternative adjusted weigt considered for te PHS was defined as follows: W j ' = W j i ε W ^ Y ', were: W j = adjusted weigt for te j-t sample ouseold (different for categories A or B) in te i-t sample SEA in stratum (district) W j = original weigt for te j-t sample ouseold in te i-t sample SEA in district ^ Y = estimated total number of rural ouseolds in district for year Y, based on demograpc projections using 1990 and 2000 Census data 5

10 W = n = weigt for te i-t sample SEA in district (inverse of probability of selection of sample SEA) = total number of ouseolds in te PHS frame for district based on te 1990 Census n = number of sample SEAs selected for te PHS in district = total number of ouseolds in te PHS frame for te i-t sample SEA in district based on te 1990 Census = total number of ouseolds listed in te i-t sample SEA in district for a particular PHS, including non-agricultural ouseolds; ts information would ave to be obtained from te original listing data Te second alternative adjusted weigt was defined as follows: W j Y n ' = Wj W ' ^ Substituting te formula for W, ts adjusted weigt can be expressed as follows: W j ' = W j n ^ Y n ' Y = Wj ^ ' Te first component of te adjustment factor is te ratio of te projected total number of inscope (rural) ouseolds in te district divided by te corresponding total number of ouseolds from te original PHS frame for te district; ts can be considered te growt rate for te rural ouseolds in te district. Te second component of te adjustment factor is te ratio of te number of ouseolds in te sample SEA from te frame divided by te corresponding number from te updated listing. In ts case, if te number of ouseolds listed in te SEA goes up, tere would be a corresponding downward adjustment in te weigt. Next, let us examine te effect of te second alternative weigt adjustment factor on te weigted number of ouseolds in eac sample SEA witn a district. Te weigted number of Category A ouseolds in a sample SEA can be calculated as follows: W j ^ ^ ^ Y A Y Y ma = ma = ' n m ' n ' A A, 6

11 were: m A = number of sample ouseolds in Category A selected in te i-t sample SEA in district A = total number of ouseolds listed in Category A in te i-t sample SEA in district All of te Category B ouseolds listed in te sample SEA will be selected (tat is, m B = B ), so te weigted number of category B ouseolds in te SEA can be calculated as follows: W j ^ ^ ^ Y Y Y mb = 1 B = ' n ' n ' B Summing te weigted number of ouseolds in Categories A and B for te sample SEA and substituting B = A, we ave: n ^ ^ ^ Y A Y + ' n ( ' A ) = ' Tat is, te effect of te second alternative weigt adjustment procedure is to make te weigted number of sample ouseolds from eac sample SEA witn a district te same, regardless of any differential growt rates or te number of ouseolds listed in Categories A and B. In oter words, it cancels any differential growt rate and assumes tat all sample SEAs witn a district ave te exact same growt rate over time. n On te oter and, te first weigt adjustment factor allows te weigted estimate from eac sample SEA to reflect te differential growt rate of te SEA. Terefore ts metod would be less biased tan te second alternative if tere is an actual differential growt in te sample SEAs witn a district, reflected by an accurate listing. However, if te difference between te number of ouseolds listed in te sample SEA and te corresponding number of ouseolds in te frame is due to variability in te quality of te coverage of te listing (instead of an actual increase or decrease in te number of ouseolds), te second alternative weigt adjustment factor may be less biased. At ts point a modified version of te second alternative weigt adjustment procedure is recommended, given te variability in te quality of te listing coverage by sample SEA, as well as a differential ouseold non-contact rate by SEA wc also affected te previous weigted estimates of te total number of agricultural ouseolds. Ts modified weigt adjustment procedure is defined next. Y 7

12 5.2. Proposed odified Weigt Adjustment Procedure Based on Projected Number of Rural Agricultural Houseolds Te proposed modified PHS weigt adjustment procedure is based on te projected number of agricultural ouseolds in eac district, using te number of agricultural ouseolds from te 2000 Census data as te bencmark. Table 2 sows te total number of agricultural ouseolds in eac district from te 1990 and 2000 censuses, as well as te corresponding percent of rural ouseolds wit agricultural operations. It can be seen tat te percentage of agricultural ouseolds in te rural areas was only 58.1 percent based on te 1990 Census data, compared to 87.9 percent from te 2000 Census data. Based on discussions wit CSO staff, tere appears to be a consensus tat te quality of te data on agricultural ouseolds from te 2000 Census is fairly good. On te oter and, te corresponding data from te 1990 Census appears to suffer from a downward bias. One possible reason for ts situation is tat te 1990 Census form only included a screening question to identify agricultural ouseolds. Wen an agricultural ouseold was identified, an agricultural supplement form was administered to te ouseold, representing a greater workload for te census enumerator; ts process could act as a disincentive for some census enumerators to identify agricultural ouseolds. Given te potential undercount of agricultural ouseolds in te 1990 Census, ts information cannot be used as te baseline for determining te growt rate for te rural agricultural ouseolds in eac district. However, te total number of rural ouseolds in te 1990 and 2000 Censuses can provide a good indicator of te growt rate for te rural ouseolds, wc are mostly agricultural. Terefore te proposed modified weigt adjustment procedure uses te growt rate for te total number of rural ouseolds between te 1990 Census and te 2000 Census, and applies ts growt rate to te 2000 Census number of rural agricultural ouseolds (mostly retrospectively) to project (estimate) te number of agricultural ouseolds in eac district for te PHS reference period. As mentioned previously, te PHS sampling frame based on te 1990 Census does not correspond exactly to te rural census frame, but it is fairly close, as sown in Table 2. For particular districts were tere is a more pronounced difference between te 1990 and 2000 Census data on te total number of rural agricultural ouseolds, te growt rate in te rural ouseolds between 1990 and 2000 may be unrealistic because of inconsistent coding of some rural areas. Terefore it was decided to use te 1990 Census data for te PHS frame as te baseline for calculating te growt rate for rural ouseolds in eac district instead of te corresponding 1990 Census rural frame. For example, in te case of Cngola District te total number of rural ouseolds in te 1990 Census was only 298, since only tree CSAs were coded as rural, compared to fifteen CSAs in te 1990 PHS sampling frame (wit a total of 3,871 rural ouseolds). Te corresponding number of rural ouseolds in Cngola District from te 2000 Census is 4,955, wc is more consistent wit te PHS frame. Te recommended PHS adjusted weigts are a modification of te second alternative metod described previously. In ts case bot te numerator and denominator of te weigt adjustment factor corresponds to te number of agricultural ouseolds, so any nonagricultural ouseolds are excluded from tese calculations. Te proposed adjusted weigt can be expressed as follows: W j AY n ' = Wj, Wj ε ^ ja 8

13 were: W j = original weigt for te j-t sample ouseold in te i-t sample SEA in stratum ^ AY = projected number of rural agricultural ouseolds in year Y for district ; te metodology for te projections is described below n = number of sample SEAs selected in district A = set of sample PHS agricultural ouseolds in te i-t sample SEA in district Te denominator of ts adjustment factor is te sum of te original weigts for all te agricultural ouseolds (in bot Categories A and B) in te i-t sample SEA in district. Table 3 of Annex I presents te number of sample SEAs by district (n ) for te PHS eac year. It can be seen tat only two sample SEAs were selected for some of te smaller districts, and in some years only one of te sample SEAs in a district were enumerated for te PHS. As a result, te estimates for suc districts cannot be considered reliable, and te corresponding adjusted weigt adjustment factors are more subject to variability. In te case Kabwe Urban District, tere is no PHS sample for years prior to te 95/96 PHS. Tere was also no PHS sample for Luansya and ifumbwe Districts in particular years. In tese cases tere is no contribution to te survey total estimates from tese districts, but given te small size of tese districts ts would ave a very minor effect on te overall PHS estimates. For te earlier years of te PHS data series, rural non-agricultural ouseolds are included in te data sets. In ts case te weigt for te agricultural ouseolds in Category A for a particular sample SEA can also be applied later to te non-agricultural ouseolds in te same SEA, since we are assuming te same growt rate for rural agricultural and nonagricultural ouseolds etodology for Estimating Projected Number of Rural Agricultural Houseolds Based on 1990 and 2000 Census Data In order to project te total number of rural agricultural ouseolds in eac district for a particular PHS it is necessary to determine te appropriate reference date for te survey population. Since te frame for selecting te sample ouseolds for eac PHS is based on te listing, initially te approximate mid-point of te corresponding listing operation was used as te reference date for te projections. From 1990/91 to 1998/99 te listing operation was conducted mostly in February, prior to te CFS. Te same sample of ouseolds selected for te CFS was used later in te year (around October) for te PHS. For te 1999/2000 agricultural season no CFS was conducted; te listing for te PHS was conducted in August. Due to limited resources, ts same listing was used for te PHS in 2000/01 and 2001/02. In order to improve te analysis of te PHS data series, it is recommended to standardize te reference date for all years of te PHS. Conceptually, it would be ideal for te reference period for eac PHS to represent te beginning of te peak arvest season for most crops. After examining te arvesting patterns, tere was a consensus among te analysts tat a 9

14 reference date of 1 ay would be appropriate eac year for estimating te projected total number of rural agricultural ouseolds for adjusting te corresponding PHS weigts. Given te exponential nature of population growt, an exponential growt model was used for calculating te projected total number of rural agricultural ouseolds in eac district for te corresponding PHS reference date eac year. Te exponential growt rate for all rural ouseolds in eac district based on te 1990 and 2000 Census data was applied (mostly retrospectively) to te total number of agricultural ouseolds in te district from te 2000 Census data. Te following formula was used to calculate te projected total number of rural agricultural ouseolds in eac district for a particular PHS reference period, using an Excel spreadseet: ^ = e AY were: 00 A ln t t t t 00 Y A = total number of rural agricultural ouseolds in district from 2000 Census 00 = 90 = t 00 t Y = t 00 t 90 = total number of rural ouseolds in district from 2000 Census total number of rural ouseolds in district from 1990 Census number of days between te 2000 Census reference date, 1 August, 2000 (t 00 ), and te reference date for te PHS listing (t Y ) number of days between te 2000 Census reference date (t 00 ) and te 1990 Census reference date (t 90 ); tat is, 3653 days Table 4 of Annex I sows te projected total number of rural agricultural ouseolds for eac PHS year by district, calculated using te formula specified above. In te case of Kabwe Urban District, tere are no rural ouseolds, but some CSAs wit rural caracteristics were included in te 1990 PHS sampling frame. Since we do not ave a corresponding number of rural ouseolds for Kabwe Urban District from te 2000 Census, ts was estimated by applying te overall average growt rate for rural ouseolds (44.5 percent) to te number of ouseolds in te PHS frame based on te 1990 Census. Te number of rural agricultural ouseolds in 2000 for Kabwe Urban District was estimated by applying te percent of agricultural ouseolds for Kabwe Rural District (84.5 percent) to te estimated total number of rural ouseolds for Kabwe Urban District. Table 4 also sows te percent difference between te projected total number of rural agricultural ouseolds at te national level eac year and te corresponding PHS estimates based on te original weigts from Table 1. It can be seen tat te weigted PHS estimates begin 7 percent ger tan te corresponding projections for te 1990/91 PHS; ts is te only year for wc te weigted PHS estimate is ger tan te projection. Te following year te PHS estimate is lower tan te projections by 37 percent. Te difference reaces a peak of 54.8 percent for te 1994/95 PHS, followed by te lowest difference of 4.1 percent for te 1995/96 PHS. Ten tere is a steady increase in te difference for te following years, reacng 43.3 percent for te 2001/02 PHS. 10

15 6. POSSIBLE REFINEENTS OF ADJUSTED PHS WEIGHTS Te accuracy of te PHS adjusted weigts depends on te quality of te weigt adjustment model and te projections for te number of rural agricultural ouseolds. Issues regarding te assumptions for te weigt adjustment procedure were described previously; for example, te model assumes tat all sample SEAs witn a district experience te same growt rate. Te CSO and analysts can review te projections by district and PHS year appearing in Table 4 and make any adjustments if more accurate information becomes available for some districts. Ten te corresponding modified projections can be copied into te weigting spreadseet and te formulas will automatically adjust te weigts accordingly. Te original and adjusted PHS weigts were examined to identify any extreme cases. In one case (Clubi District, 95/96 PHS) te original weigt was 0, and a few oter original weigts were less tan 1. Some of te original weigts were corrected, and any remaining original or adjusted weigt tat was less tan 1 was canged to equal 1, so tat te sample ouseolds in te corresponding SEAs will at least represent temselves in te weigted survey estimates. Te largest weigts and adjustment factors were also examined. Te largest weigt, , was found in a sample SEA wit only one agricultural ouseold. Some oter large adjusted weigts correspond mostly to districts wit a very small PHS sample, especially in years wen only one SEA is included in te sample. Te maximum weigt adjustment factor is for te sample SEA in Clubi for wc te original weigt was increased from 0 to 1; terefore te corresponding adjusted weigt is Ts is probably a more reasonable weigt anyway, since te weigt of 1 was arbitrary. All te oter weigt adjustment factors are less tan 50; te gest values are generally in sample districts wit a very small PHS sample or in SEAs wit few agricultural ouseolds. It is possible to set a limit for te weigt adjustment factors, altoug te resulting weigted estimates for te smaller districts may no longer closely follow te projections. Any minor adjustments may not ave muc impact on te overall survey results. 11

16 7. REVIEW OF THE PERCENTAGE OF AGRICULTURAL HOUSEHOLDS IN PHS FRAE As mentioned previously, te PHS listing metodology was canged to exclude nonagricultural ouseolds starting wit te 1999/2000 PHS. In order to determine te percentage of agricultural ouseolds in te PHS frame eac year, te adjusted weigts were used to estimate te total number of ouseolds and agricultural ouseolds by district. Te resulting percent of agricultural ouseolds in te PHS frame eac year by district is presented in Table 5 of Annex I. It is interesting to note tat in te early years of te PHS wen all rural ouseolds were included in te PHS, te percent of agricultural ouseolds was fairly g. Te lowest percent is 94.1 for te 1993/94 PHS. Te corresponding estimate from te 2000 Census was 87.9 percent agricultural ouseolds in te rural areas. As expected, te percent increased to over 99 starting wit te 1999/00 PHS, wen only agricultural ouseolds were supposed to be selected for te survey. One exception is in te small district of Livingstone, were only 77 percent of te ouseolds in te 2001/02 PHS sample were agricultural ouseolds. Peraps tere are more non-farm economic activities available in te rural areas of ts district. Te large percentage of agricultural ouseolds in te early years of te PHS could represent an empasis on covering agricultural ouseolds in te listing. Tere is also te issue of te definition of an agricultural ouseold implemented in te field, but te same criteria were used for counting te agricultural ouseolds in eac PHS data set for Table 5. Tere is also a possibility tat te 2000 Census sligtly underestimated te number of agricultural ouseolds in te rural areas, depending on te definition used for agricultural ouseolds. 12

17 8. WEIGHTS FOR THE 2004 PHS SUPPLEENTAL PANEL SURVEY In 2001 a Supplemental Survey was conducted using te panel of te sample ouseolds selected for te 1999/2000 PHS. All of te sample ouseolds in te 1999/2000 PHS tat were found in te sample SEAs in 2001 were included in te sample for te Supplemental Survey. Te 2004 Supplemental Survey followed ts same panel of sample ouseolds tree years later to provide additional longitudinal data for tese ouseolds. Te main objective of te Supplemental Surveys was to provide longitudinal data for te sample ouseolds in te panel tat can be used to study micro-level canges in agricultural practices and socioeconomic status over time. Te correlation in te sample data between te Supplemental Surveys and te 1999/2000 PHS will also improve te precision of te estimates of trends over time for relative indicators suc means and proportions. In developing te weigting procedures for te 2001 and 2004 Supplemental Surveys, it is important to first qualify te population represented by te panel of sample ouseolds. Since ts panel was based on te sample selected for te 1999/2000 PHS from a listing conducted in August 1999, it represents te ouseolds from tat period wc still existed in te same geograpc location at te time of eac Supplemental Survey. For example, in te case of te 2001 Supplemental Survey, te sample represents more tan 94 percent of te agricultural ouseolds in te 1999/2000 PHS frame. However, te panel does not represent any newer ouseolds or tose tat moved between 1999 and Given te attrition in ts panel of sample ouseolds over time, ts sample represents less of te current population eac year. Given tat te frame for te Supplemental Surveys was te sample of ouseolds selected for te 1999/2000 PHS, te adjusted weigts for eac Supplemental Survey will be based on te adjusted weigts for te 1999/2000 PHS. Tese weigts were calculated as specified previously, tat is, based on te projected total number of rural agricultural ouseolds for te reference date of ay 1, Te number of sample ouseolds in te panel decreased for eac Supplemental Survey because of attrition and non-interviews. It is necessary to adjust te 1999/2000 PHS weigts for sample ouseolds wc existed in te sample SEAs at te time of te Supplemental Survey but were not interviewed due to refusals or noncontacts (suc as no respondent available at ome). However, te ouseolds wc moved or were dissolved would no longer be considered part of te frame represented by eac Supplemental Survey, so tese ouseolds would be excluded from te sample SEA frame in calculating te non-interview adjustment factor for eac sample SEA and category. In oter words, te estimate of te total number of rural agricultural ouseolds from eac Supplemental Survey data set based on te adjusted weigts will be equal to te corresponding 1999/2000 PHS weigted estimates minus te weigted estimate of te total number of agricultural ouseolds tat no longer existed in te same location. Te proposed adjusted weigts for te 2001 Supplemental Survey can be expressed as follows: W n m d = W c AS01 A00 00 S 01 S01 S01, were: 13

18 W AS01 = W A00 = n 00 = m S01 = d S01 = adjusted weigt for te sample ouseolds in te 2001 Supplemental Survey for te i-t sample SEA (by size category) in stratum (district) adjusted weigt for te 1999/2000 PHS sample ouseolds in te i-t sample SEA (by size category) in district number of ouseolds in te 1999/2000 PHS sample for te i-t sample SEA in district number of sample ouseolds tat moved from te i-t sample SEA in district prior to te 2001 Supplemental Survey number of sample ouseolds in te i-t sample SEA in district tat were dissolved prior to te 2001 Supplemental Survey c S01 = number of sample ouseolds wit completed interviews for te 2001 Supplemental Survey in te i-t sample SEA in district Te recommended adjusted weigt for te 2004 Supplemental Survey can be expressed as follows: W n m d m d = W c AS04 A00 00 S 01 S 01 S 04 S04 S04, were: W AS04 = m S04 = d S04 = adjusted weigt for te sample ouseolds in te 2004 Supplemental Survey in te i-t sample SEA (by size category) in stratum (district) number of sample ouseolds tat moved from te i-t sample SEA in district prior to te 2004 Supplemental Survey number of sample ouseolds in te i-t sample SEA in district tat were dissolved prior to te 2004 Supplemental Survey c S04 = number of sample ouseolds wit completed interviews for te 2004 Supplemental Survey in te i-t sample SEA in district After generating tese adjusted weigts for te 2001 and 2004 Supplemental Surveys, te weigted total number of ouseolds by district for eac survey was tabulated and compared to te corresponding results from te 1999/2000 PHS. Table 6 of Annex I sows te estimated total number of ouseolds from eac Supplemental Survey and te percentage of te 1999/2000 PHS frame tat is represented by eac survey. It can be seen tat at te national level te 2001 Supplemental Survey represents 94.2 percent of te 99/00 PHS frame, wle te corresponding percent for te 2004 Supplemental Survey is Tat is, it is estimated tat sligtly more tan 20 percent of te rural ouseolds moved or were dissolved between te 1999/2000 PHS and te 2000 Supplemental Survey. 14

19 9. RECOENDED CHANGES IN THE LISTING AND WEIGHTING PROCEDURES FOR FUTURE PHS AND CFS As indicated previously, one of te problems wit te listing procedures for te PHS is tat te non-contact ouseolds were not accounted for in te estimation procedures. Ts can lead to a downward bias in te estimates of te total number of agricultural ouseolds, total crop and livestock production, etc. Altoug te weigt adjustment metodology will offset part of te deficiencies in te listing procedures, it is only a temporary solution and is also subject to bias, since it depends on te quality of te projected number of agricultural ouseolds and various assumptions. Terefore it is critical to improve te quality of te listing procedures for te future PHS and CFS. Te first step in improving te coverage of te listing of ouseolds would be to update te sample SEA sketc maps in order to clarify te SEA boundaries, so tat te areas covered by te listing are consistent wit te boundaries defined for te census. Additional landmarks can be introduced on te sketc maps to better identify te SEA boundaries. Identifying te location of eac ousing unit on te sketc map sould also elp. Anoter important quality control procedure is to compare te total number of ouseolds listed in eac sample SEA to te corresponding number from te 2000 Census. Te district supervisor sould be provided wit information on te number of ouseolds enumerated in te sample SEAs for te 2000 Census for verification purposes. Any large discrepancy between te number of ouseolds enumerated in te census and listing operation for te sample SEA sould be accounted for to determine weter it is due to a large movement of ouseolds in or out of te SEA, or to poor quality of te enumeration. Te CSO is also considering te possibility of aving te listing operation conducted by a separate staff wit cartograpc experience, in order to improve te quality of te listing. Ts sould improve te coverage of te listing, as long as it is introduced togeter wit te additional quality control procedures. In order to correct for te bias in te previous weigting procedures, it will be necessary to modify te listing procedures to account for all ouseolds witn te boundaries of eac sample SEA, including te non-agricultural ouseolds and non-contacts. Previously only te ouseolds in categories A, B and C (tat is, agricultural ouseolds) were taken into account. Te information on te total number of listed ouseolds will be used to adjust te weigts for te sample ouseolds in categories A, B and C. Te following weigt adjustment factor sould be applied to te weigts for all sample ouseolds witn a sample SEA: F = A + B + C + NA + NC A + B + C + NA, were: F j = A = weigt adjustment factor for non-contacts in te i-t sample SEA in stratum (district) total number of ouseolds listed in category A in te i-t sample SEA in district 15

20 B = C = total number of ouseolds listed in category B in te i-t sample SEA in district total number of ouseolds listed in category C in te i-t sample SEA in district NA = total number of non-agricultural ouseolds listed in te i-t sample SEA in district NC = total number of non-contact ouseolds (witout listing information) in te i-t sample SEA in district Te numerator of ts weigt adjustment factor is te total number of ouseolds listed in te sample SEA, including non-agricultural and non-contact ouseolds. Ts weigt adjustment factor at te sample SEA level will ave te same effect as a proportional allocation of te number of non-contact ouseolds between te tree categories of agricultural ouseolds and te non-agricultural ouseolds. Te reason tat te non-agricultural ouseolds ave to be included in te listing is to account for te total number of ouseolds for ts adjustment procedure, even toug tey will not be included te sample for te PHS and te CFS. One problem in reviewing te current weigts for te PHS is tat some of te information used for calculating te weigts for past PHS surveys is missing, and te listing information is also not available. For eac PHS and CFS, it is very important to arcve all te information from te sampling frame and listing used for calculating te weigts. Secure backups of all te files sould also be maintained. 16

21 10. CONSIDERATION FOR SPECIAL CROP WEIGHTS Tere is some concern about te PHS estimates for certain crops tat are gly localized, given te potentially large sampling errors for suc crops. In te past te CSO ad calculated special crop weigts for suc crops tat are only found in certain parts of a district. In ts case, tey post-stratified te CSAs witn eac stratum (district) into two groups based on information from te 1990 Census frame: CSAs wc ave ouseolds wit te specified crop in te frame, and tose witout. Te weigt for eac localized crop was ten modified as follows: W were: N X = m X N XC N n C C, W XC = weigt for localized crop X in sample ouseolds in farm size category C in te i-t sample SEA in stratum N X = total number of ouseolds in te frame for te CSAs wit crop X witn stratum m X = number of sample CSAs wit crop X in te frame witn stratum N = total number of ouseolds in te frame for te i-t sample SEA in stratum N C = total number of ouseolds in farm size category C from te listing for te i-t sample SEA in stratum n C = number of sample ouseolds selected in farm size category C from te listing for te i-t sample SEA in stratum Tere is some question as to weter tese special crop weigts were implemented in te PHS tabulations. In te case of te future PHS estimation procedures, it is important first to examine te tabulations based on te original weigts and te corresponding sampling errors. Suc crop weigts may be considered in te future wen certain crops are only found in part of a district and te resulting sampling errors are g. Ts crop weigting procedure could be refined furter by cecking te crops in te frame at te SEA level, and redefining te terms N C and m C as follows: N= C = total number of ouseolds in te frame for te SEAs wit crop C witn stratum m= C = number of sample SEAs wit crop C in te frame witn stratum It may also be possible to improve te survey estimates troug ratio estimation in te case of crops for wc independent data are available from oter sources suc as frames maintained by te inistry of Agriculture, processing plants or farming associations. 17

22 Ratio estimation involves te use of independent information for a survey variable suc as area planted for a particular crop. For example, it can be used to estimate total crop production wen te total area planted for te crop is known from anoter source. In ts case, te average crop yield would be estimated from te survey data and ten multiplied by te total area planted, as follows: Pˆ ( = ( i W W j j Cj i C y x Cj ) ) X C, were: y Cj = production of crop C for te j-t sample ouseold in te i-t sample SEA in stratum x Cj = area planted for crop C for te j-t sample ouseold in te i-t sample SEA in stratum X C = good estimate of total area planted in crop C from independent source Te first term represents te survey estimate of te average crop yield per ectare. Of course, one limitation of ts ratio estimation procedure is te availability of accurate information on te total area planted for te particular crop. However, suc data may be available for particular crops suc as tobacco for wc tere may exist farmer associations or special arrangements wit a factory. In oter cases suc as cotton, an accurate figure for crop production may be available from a processing or marketing company. In ts case te total production of cotton from te independent source can be divided by te survey estimate of te average yield for cotton in order to estimate te total area planted in cotton. 18

23 ANNEX I. Table 1. Tables for Review of PHS Weigting etodology Weigted Estimate of Total Number of Agricultural Houseolds for Eac PHS by District, Based on Original Weigts PROVINCE OLD DISTRICTS Post-Harvest Survey Year 90/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/00 00/01 01/02 CENTRAL 11 Kabwe Rural 29,578 26,594 25,751 26,495 25,462 33,402 38,695 32,325 31,099 27,040 24,314 24, Kabwe Urban 2,007 2,167 1,995 2,053 1,583 1,647 1, kus 18,245 15,891 15,324 17,910 15,826 19,203 13,664 16,989 17,072 11,354 11,338 11, umbwa 18,740 16,100 16,682 15,002 16,919 16,518 15,977 16,105 16,251 13,857 13,513 13, Serenje 16,095 14,151 16,860 15,025 15,079 19,322 19,364 19,964 19,098 17,082 16,977 16,977 COPPERBELT 21 Clilabombwe 2,633 1,645 1,960 1,261 3,890 1,770 1,836 1,506 1,418 1,374 1,457 1, Cngola ,147 2,378 2,422 1,038 1,475 1,307 1, Kalulus 3, ,073 1,153 2,689 2,737 2,658 2,328 2,626 2,419 2, Kitwe ,017 2,129 3, ,361 1,517 1,067 1,011 1, Luansya 4,937 3,116 5,140 3,279 2,061 1,750 2,809 2,746 1,803 1,890 1, ufulira 4,587 2,979 2,440 1,044 2,504 2,936 2,175 2,752 2,896 1,477 1,483 1, Ndola Rural 30,198 19,147 23,313 19,743 23,426 27,280 27,044 26,184 25,925 24,718 21,075 24,769 EASTERN 31 Cadiza 11,785 9,056 10,830 9,974 9,612 14,280 12,781 12,568 14,592 14,440 14,281 14, Cama 9,653 7,596 5,304 4,016 1,999 6,678 8,248 12,707 11,991 12,566 12,417 12, Cpata 44,470 33,562 41,720 41,533 33,862 58,185 57,359 57,996 51,977 52,711 53,499 53, Katete 27,463 21,389 20,958 20,318 21,087 32,195 32,118 31,629 31,339 32,134 32,799 32, Lundazi 33,752 27,131 23,942 25,914 22,169 29,353 29,422 28,408 29,938 30,241 33,024 29, Petauke 44,953 35,161 37,018 35,466 33,843 45,977 56,911 51,900 50,114 46,533 47,055 46,376 LUAPULA 41 Kawambwa 14,313 11,764 11,640 11,745 10,730 19,291 18,453 18,401 17,994 16,375 16,430 16, ansa 21,096 13,360 17,107 14,869 15,669 22,732 21,680 26,165 25,756 21,874 20,643 20, wense 15,159 10,416 10,394 10,317 10,545 18,028 19,209 16,967 18,055 15,768 15,951 15, Ncelenge 18,454 10,329 9,340 11,233 8,730 27,756 25,841 27,946 30,788 27,640 28,816 28, Samfya 19,328 9,712 7,722 12,471 11,875 29,446 29,563 38,189 37,241 25,056 25,115 25,171 LUSAKA 51 Luangwa 2,880 2,790 3,996 2,202 1,098 2,394 2,508 2,133 2,544 2,176 2,176 2, Lusaka Rural 21,952 18,892 16,328 19,625 19,232 25,330 20,984 20,448 19,672 15,089 16,778 16,753 1

24 Table 1. Weigted Estimate of Total Number of Agricultural Houseolds for Eac PHS by District, Based on Original Weigts (Continued) PROVINCE OLD DISTRICTS Post-Harvest Survey Year 90/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/00 00/01 01/02 NORTHERN 61 Clubi 8,504 5,204 4,281 6,356 6,423 8,273 9,389 10,387 11,716 6,166 4,182 4, Cnsali 15,924 11,083 10,507 11,120 12,170 17,172 17,785 16,490 17,421 15,957 15,894 15, Isoka 23,581 15,969 12,465 16,314 13,797 22,803 23,192 23,339 22,776 17,585 17,589 17, Kaputa 8,321 5,133 6,327 5,984 6,170 12,358 12,660 13,760 12,225 13,018 13,607 12, Kasama 25,920 18,074 22,410 21,278 19,520 38,602 39,173 37,618 41,498 24,399 22,670 24, Luwingu 11,852 7,584 7,608 8,078 10,227 12,280 12,680 14,401 14,383 12,135 12,373 11, bala 16,895 14,151 14,182 15,499 15,414 25,195 24,956 27,665 27,557 22,478 22,239 22, pika 16,989 11,863 11,508 10,977 11,246 17,639 19,055 16,621 18,559 15,133 14,903 15, porokoso 10,704 7,473 7,817 7,710 7,710 8,835 8,835 8,631 9,239 9,667 9,667 9, ufumbwe 3,203 2,253 4,462 5,140 2,657 2,436 2,034 3,108 1,766 1,766 1, Kabompo 10,294 6,772 6,232 6,456 5,930 10,346 10,349 9,637 9,753 9,353 9,253 9, Kasempa 6,428 4,260 3,541 5,890 4,014 7,619 7,705 5,753 5,033 5,790 5,665 5, winilunga 15,389 10,748 12,580 13,429 13,419 13,416 15,652 16,498 14,311 15,052 14,475 14, Solwezi 19,745 12,976 14,791 13,314 11,119 11,651 11,535 10,727 11,931 9,176 9,176 9, Zambezi 15,571 10,286 5,242 7,314 5,572 9,465 13,021 12,278 12,680 9,243 8,929 9,361 SOUTHERN 81 Coma 19,346 13,614 13,656 13,568 16,728 20,408 20,293 21,018 23,669 18,676 19,213 18, Gwembe 5,437 2,943 1,499 4,382 1,968 4,000 3,949 4,291 4,714 5,359 5,359 9, Kalomo 22,391 16,256 13,752 16,495 13,668 22,799 22,821 26,480 29,530 23,283 19,303 22, Livingstone 1, ,874 1,207 1,207 1,450 1, , , azabuka 16,571 11,649 15,429 15,019 11,248 21,023 20,586 21,244 23,278 19,661 17,744 19, onze 14,273 10,032 7,758 10,035 9,395 20,563 22,085 20,961 21,626 18,788 18,788 18, Namwala 11,826 8,316 3,635 5,275 3,632 13,679 11,065 10,728 11,342 11,252 11,135 11, Siavonga 4,543 4,514 5,818 3,054 2,223 1,312 2,512 2,359 2,611 4,272 4,286 4, Sinazongwe 9,512 6,714 9,153 6,708 5,543 8,502 8,242 7,923 7,784 8,659 8,659 8,659 WESTERN 91 Kalabo 19,498 10,307 8,445 9,150 9,461 14,231 14,649 13,003 16,271 13,510 13,360 13, Kaoma 19,021 10,246 8,560 16,556 15,445 24,451 26,229 26,078 23,871 21,928 21,720 21, Lukulu 9,899 4,305 2,607 5,469 4,542 14,068 15,421 14,804 13,608 10,871 10,871 10, ongu 23,014 12,385 15,060 16,019 11,351 15,651 18,824 18,645 21,817 19,921 20,139 19, Senanga 25,264 13,563 17,223 12,908 13,092 22,307 14,861 13,410 14,599 16,663 16,772 16, Seseke 11,181 6,918 6,585 5,885 6,336 11,704 21,206 20,960 21,602 19,850 19,580 19,976 ZABIA 837, , , , , , , , , , , ,503 2

25 Table 2. Distribution of Total Number of Rural Houseolds and Agricultural Houseolds in te 1990 and 2000 Zambia Censuses, and te PHS Frame Based on te 1990 Census Data Province District Total No. of Rural Houseolds Percent Census Census Cange Total No. Houseolds in PHS Frame Census Difference, No. Hs. in PHS Frame and Rural Areas - Rural Agricultural Houseolds from Census Data 1990 Census 2000 Census No. Agric. Hs. % Agric. Hs. No. Agric. Hs. % Agric. Hs. CENTRAL 11 Kabwe Rural 32,291 70, % 32, , % 59, % 12 Kabwe Urban 0 0-2,559 2, kus 16,923 17, % 16, , % 14, % 14 umbwa 17,505 23, % 17, , % 20, % 15 Serenje 14,903 21, % 14, , % 19, % COPPERBELT 21 Clilabombwe 1,897 2, % 2, % 2, % 22 Cngola 298 4,955 1, ,871 3, % 4, % 23 Kalulus 2,906 4, % 2, % 3, % 24 Kitwe 474 2, % 2,733 2, % 1, % 25 Luansya 2,896 7, % 3, % 5, % 26 ufulira 2,300 4, % 3, % 4, % 27 Ndola Rural 30,670 45, % 32,584 1,914 16, % 39, % EASTERN 31 Cadiza 11,372 15, % 11, , % 14, % 32 Cama 9,505 13, % 9, , % 13, % 33 Cpata 46,039 66, % 46, , % 62, % 34 Katete 26,865 36, % 26, , % 33, % 35 Lundazi 31,164 44, % 31, , % 42, % 36 Petauke 44,650 57, % 45, , % 54, % LUAPULA 41 Kawambwa 15,269 17, % 16,881 1,612 10, % 15, % 42 ansa 22,013 34, % 21, , % 32, % 43 wense 18,078 22, % 18, , % 20, % 44 Ncelenge 22,069 38, % 24,218 2,149 13, % 27, % 45 Samfya 22,511 31, % 22, , % 28, % LUSAKA 51 Luangwa 2,999 3, % 2, , % 2, % 52 Lusaka Rural 26,198 43, % 27,892 1,694 10, % 27, % 3