Changing the way smoking is measured among Australian adults: A preliminary investigation of Victorian data

Transcription

1 Changing the way smoking is measured among Australian adults: A preliminary investigation of Victorian data Robyn Mullins Ron Borland 163

2 Quit Evaluation Studies No Introduction In 1997, the Australian Institute of Health and Welfare set up an Expert Group on the Measurement of Smoking to develop standard measures on the measurement of tobacco use in Australian adults. The measures are to be included in the National Health Data Dictionary, and it is intended that they will be used in future population surveys of smoking prevalence. Previously, there has not been an agreed method of determining smoking status in Australia. The data collected since 1974 by the Centre for Behavioural Research in Cancer is the only long-term trend line for adult smoking prevalence(from Gray & Hill 1975 to Hill, White & Scollo, 1998). It is intended that the new data standard will replace the question, which has been used for that series. As such, it is crucial that a study is conducted that allows the data to be calibrated from responses on both sets of questions. The next Australia-wide data collection is in 1998, and a major calibration study will be carried out on that data to ensure that a true trend line is being measured. In the 1997 Victorian data collection both sets of questions were included as a preliminary study. Method The household surveys are commissioned from a large market research company, which interviews a representative sample of Victorians in their own homes. The questions designed by the Centre for Behavioural Research in Cancer, form part of an omnibus survey that is conducted on weekends over an eight week period, beginning in October. The method used to collect the information in 1997 was the same as that used in previous years, and is described fully in Hill and Gray (1984), but as mentioned above an additional series of questions on smoking prevalence was also included in In this study 2365 Victorians were interviewed. Forty-eight per cent of the sample was men and 52% women. Twenty-four per cent of the sample was aged between 16 and 29 years, 38% were between 30 and 49 years and the remaining 38% were 50 years or over. 164

3 Chapter 12: Changing the way smoking is measured among Australian adults New and existing measures of smoking Until 1997, smoking prevalence was measured by a self-report question, which asked respondents to pick which of a series of statements best described them. The statements were: Smoke only cigarettes/ryo Smoke cigarettes/ryo and also cigars/pipe Smoke cigars, used to smoke cigarettes Smoke pipe, used to smoke cigarettes Smoke cigars, never smoked cigarettes Smoke pipe, never smoked cigarettes Don t smoke now, used to smoke only cigarettes Don t smoke now, used to smoke cigarettes and cigars/pipe Don t smoke now, used to smoke only cigars/pipe Never smoked at all. Responses to this were then used to divide respondents into smokers, exsmokers and never smokers, with the few unable to answer the question included with the never smokers. The question requires respondents to choose the label which they believe best describes them, rather than being proscriptive about what constitutes a smoker or ex-smoker. One advantage of this method of data collection is that it gathers a great deal of information about past and present behaviour, and the types of tobacco product smoked with just one question. The new questions asked respondents about their smoking behaviour, rather than their views on their own smoking status. The main question put to them was: Do you currently smoke any tobacco products: Daily At least once a week Less often than once a week Not at all? Those respondents who were not daily smokers were then asked Would you have smoked at least 100 cigarettes or the equivalent amount of tobacco in your life? and In the past have you ever been a daily smoker? 165

4 Quit Evaluation Studies No The first of these questions was used to determine whether a respondent was an ex-smoker or a never smoker. Results Table 1 shows how respondents surveyed in 1997 were categorised using the two measures. Table 1: Smoking status by new and existing measures (frequencies) Smoke daily At least weekly Less than weekly Not at all Total Smokers Ex-smokers Never smokers Total Table 2: Original smoking classification by new questions on past smoking behaviour Smoker Ex-smoker Never smoker Total n= 77* Smoked 100 Yes 78% 87% 4% 39% No 13% 6% 86% 53% Can t say 9% 7% 10% 9% Ever smoked daily Yes 44% 80% 1% 33% No 46% 15% 84% 56% Can t say 10% 6% 15% 11% * Low number of smokers because those who identified themselves as daily smokers were not asked about previous daily smoking or having smoked 100 cigarettes. Of the 2365 respondents, the majority were categorised in the same way on each measure, but there were some inconsistencies in the responses. 166

5 Chapter 12: Changing the way smoking is measured among Australian adults Of those who self-described as ex-smokers, six said they smoked daily and eight said that they smoked at least weekly. Of the self-described smokers, five said they did not smoke at all. There appears to be a degree of uncertainty about how to categorise themselves among those who smoke very irregularly. Forty-seven respondents said they smoked less than once a week, and of those 26 described themselves as smokers and 19 as exsmokers. These inconsistent cases are discussed in more detail later. The respondents who said they did not smoke every day (n=1836) were then asked questions about smoking of 100 cigarettes or tobacco and their previous daily smoking. Table 2 shows how respondents classified themselves on the original measure and how they rated previous daily smoking and the amount they had smoked. There were few people who described themselves as never having smoked who reported having smoked daily (1%) or having smoked 100 cigarettes (4%). Four out of five ex-smokers had been daily smokers at some point, and 87% said they had smoked at least 100 cigarettes. There seems to be an element of confusion about what constitutes daily smoking among some of those who have been light smokers in the past, as more were unable to answer the question on daily smoking (11%) than the one on smoking of 100 cigarettes (9%). While they know they have smoked fewer than 100 cigarettes, they are unsure of whether they were ever daily smokers. Table 3 presents the cross tabulation of the questions on having smoked daily and having smoked 100 cigarettes, broken down by current smoking status. As the data in Table 3 indicate, there was a significant number of respondents who could not answer either question, with 146 (8%) who were unable to say either if they had ever smoked daily or if they had smoked 100 cigarettes. Nearly all of those who were unable to answer this question described themselves as not smoking at all at present (140 respondents). Almost half were over 50 (71 respondents), so poor recall may account for some of this response. Those who were unable to answer the questions predominantly described themselves as never smokers (103) on the old measure, with some saying they were ex-smokers (37) and a few that they were smokers (6). It would seem a reasonable assumption that respondents who had not smoked 100 cigarettes, or were unable to say if they had ever smoked 100 cigarettes, would not describe themselves as ever having been daily 167

6 Quit Evaluation Studies No smokers, but this was not the case for 13 people. There is little we can say to categorise these people, except that all but one of them described themselves as ex-smokers. The other said he or she had never smoked. There were 121 respondents who said they had never smoked daily, but who had smoked at least 100 cigarettes, indicating low levels of smoking at some time. Table 3: Previous daily smoking by smoking of 100 cigarettes among non-daily smokers (frequencies) Ever smoked daily Yes No Can t say At least weekly Smoked 100 Yes No 1 Can t say 4 Less than weekly Smoked 100 Yes No 8 Can t say 1 2 Not at all Smoked 100 Yes No Can t say Total Analysis of the inconsistent cases As described above, the majority of respondents were classified in the same way on each of the measures of current smoking (Table 1). There were however some inconsistencies, and it is important to determine which of the measures most accurately described those respondents smoking. 168

7 Chapter 12: Changing the way smoking is measured among Australian adults On the old measure there were 14 people who self-described as exsmokers and one who said he or she never smoked, who then said that they smoked at least weekly on the new measure. On the basis of their response to the new measure, these people were asked questions intended for smokers, so their responses to these questions will help to identify where they should be correctly classified for example, someone who has never smoked would be unable to answer a question on intention to quit. All seven of the non-smokers on the old measure who said they smoked daily were able to give a sensible estimate of the number of cigarettes they smoked each day (ranging from 4 to 35), and also had valid responses to questions about previous attempts to quit and intentions of quitting. These people were clearly more accurately classified under the new measure. Of the eight classified as ex-smokers on the old measure but as smoking weekly on the new measure, five were able to give an estimate of the number of cigarettes they smoked per week. For each of these this was very few a maximum of 12, but all the rest estimated fewer than six per week. Another two could not estimate how many they smoked each week, but were able to give a valid response to the question about their intention to quit, suggesting they must smoke. This suggests that seven of the eight were best classified as weekly smokers, and the appropriate classification of one is unknown. There is also a group of respondents who described themselves as smokers on the original measure, but who then said they smoked less than weekly (26) or not at all (5). The five were not asked any of the questions aimed at smokers, so we cannot see how they responded to them, but the 26 less than weekly smokers were asked detailed questions about their consumption of specific tobacco products, namely factorymade cigarettes, roll your own cigarettes, cigars, pipes and any other tobacco products. Two of the 26 indicated they smoked cigarettes daily and one that he or she smoked at least weekly, but the other responses were all quite consistent although these people saw themselves as smokers they did not smoke any tobacco product more than once a week. Only eight of these respondents said they had ever smoked daily, but 17 had smoked at least 100 cigarettes. There appear to be three respondents who are misclassified. These data indicate that there is some variation in the way that people who smoke at very low levels classify themselves, with some seeing themselves as ex-smokers and some as current smokers, but the new system works well for most. In summary, all of those who said they 169

8 Quit Evaluation Studies No smoked daily but did not describe themselves as smokers were more correctly classified under the new system, as were six of the eight at least weekly smokers who described themselves as ex-smokers. Twenty-three of the 26 who said they smoked less than weekly were most accurately classified under the new system. We do not have enough information about the less than weekly smokers who called themselves ex- or never smokers, or the smokers who smoked not at all to determine where they would be best categorised. Prevalence of smoking under the two measurement systems Under the original system, 599 of the 2365 respondents identified themselves as smokers, giving a prevalence level of 25.3%. The new method gives a slightly lower prevalence of 24.7%, when only those who are regular smokers, that is they smoke at least weekly, are counted. Another 47 people (2%) are considered to be irregular smokers, and if they are included (which is not recommended by the expert committee) prevalence estimates would be higher. It should be noted however, that in this study all respondents were asked the original question first then the new version, so any effects from the ordering of the questions have not been accounted for. The 1998 study will test for impact due to the ordering of the questions. According to the draft data standard, respondents who say they do not currently smoke at all at present are classified as ex-smokers if they have smoked 100 cigarettes in their lifetime and as never smokers if they have smoked less than that. There were 1735 people who said they did not smoke at all. Of these 622 said they had smoked at least 100 cigarettes, therefore 26.3% of the sample were classified as ex-smokers. Another 961 had not smoked 100 cigarettes so were classified as never smokers (40.6%). The draft data standard does not give directions on how to categorise the 152 (6.4%) who could not answer the question. A case could be made that these people must at least have dabbled with smoking, or they would be able to say no confidently to the question, and therefore they should be classified as ex-smokers. If they were, then 32.7% of the sample would be classified as ex-smokers, an increase over the 29.7% in the old version. We know however, that the majority of these people self-describe as never smokers, and their smoking would at most have been minor (or they would have been able to answer the questions), so they are probably best classified as never smokers. In this case, 47.0% of the sample would be classified as never having smoked compared with 44.9% in the old version. 170

9 Chapter 12: Changing the way smoking is measured among Australian adults Discussion The new categorisation of smokers makes the definition tighter and probably more accurate than the old measure did that is, it restricts smokers to those who smoke at least weekly, and picks up those who smoke at least weekly, but don t describe themselves as smokers. For those discrepant cases where we have collaborating information, the new system is clearly superior at identify smokers, but we lack any collaborating evidence in some cases, so are not yet in a position to be certain of how some respondents should best be described. It must be noted that smoking prevalence is not an absolute there is a grey area of light, infrequent smoking where people are not clearly smokers or non-smokers, and may in fact be unsure of how to describe themselves. The solution of the expert group is the inclusion of a frequency component when asking about smoking, so very light smokers can indicate they smoke even if it is less often than weekly. This allows for different categorisations of smoking to be made if desired. For normal purposes the expert group proposes combining at least weekly with daily smoking to form the category regular smokers. Those who say they smoke less than weekly called irregular smokers are considered a separate group, but can be combined with the weekly smokers to form the group occasional smokers if this categorisation is useful. It is acknowledged that there are some respondents who say they smoke not at all but who may actually smoke some form of tobacco very occasionally, but the very rare use of tobacco is effectively ignored in the classification. While the new system is an improvement over the old one for identifying and classifying smokers, there are some difficulties with the categorisation of ex-smokers and never smokers which need to be resolved. An unacceptably large number of respondents are unable to say if they have ever smoked 100 cigarettes, which leaves them uncategorised under the present system. This would not be resolved by substituting the question on ever having smoked daily for ever smoked 100 cigarettes as a greater number were unable to answer that question. Modification of the wording of the questions is needed to eliminate or dramatically reduce the number of respondents who are unable to answer it. If this cannot be achieved a decision is needed on how to classify these people. The expert committee has changed the question about having smoked 100 cigarettes to read Over your lifetime, would you have smoked 100 cigarettes or the equivalent amount of tobacco? The purpose of this is to clarify the question for those who may have thought it referred to smoking 171

10 Quit Evaluation Studies No cigarettes in a day, but we do not know if this will solve the problem for many of those who can t say. The question on ever having smoked daily might be improved by the addition of a time frame for example, In the past, have you smoked daily for 3 months? This would help those who are unsure of how to answer the question because they have smoked for a few consecutive days, but do not know if that is long enough to count as having been a daily smoker. More research is needed on the wording of this question, but it should be possible to modify it so that it is easier to answer than the one about 100 cigarettes, as people do not count the cigarettes they smoke, and their smoking will often have been many years ago. In using a criterion-based classification system to categorise respondents smoking status, we need to acknowledge that people may be classified into categories they would not self-categorise into. This may be a problem for example if a respondent is classified as an ex-smoker, and asked questions about quitting smoking, when they do not perceive they have been a smoker. There is no evidence that this has occurred here, but it needs to be kept in mind as the difficulties with the ex-smoker and never smoker categories are resolved. In conclusion, the new system appears to work well for classifying smokers. We believe more work is needed on classifying ex-smokers and never smokers, by improving the questions used. Until such work is done, those who can t say if they have smoked 100 cigarettes should be included with those who have never smoked, as this appears to accurately classify the majority of cases. 172

11 Chapter 12: Changing the way smoking is measured among Australian adults References Gray N, Hill D (1975) Patterns of tobacco smoking in Australia. Medical Journal of Australia, 22: Hill D, Gray N (1984) Australian patterns of tobacco smoking and health-related beliefs in Community Health Studies, 8: Hill D, White V, Scollo M (1998) Smoking patterns of Australian adults in 1995: trends and concerns. Medical Journal of Australia, 168:

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