Hubungan antar variabel HERTANTO WAHYU SUBAGIO

Transcription

1 Hubungan antar variabel HERTANTO WAHYU SUBAGIO

2 Hubungan antar variabel interdependensi asosiasi i korelasi regresi

3 Interdependensi * Saling ketergantungan antara X dengan Y *UjiX 2 (kai kuadrat = chi square) Tidak dapat mengetahui keeratan hubungan antara X dengan Y

4 Asosiasi * Kelanjutan dari uji interdependensi * uji : Koefisien i kontingensi i Phi Cramer s V * nilai iantara 0-1(t (tak ada - berasosiasi i sempurna) * tidak menunjukkan arah hubungan (pos / neg)

5 Korelasi * menunjukkan arah hubungan * Uji : r product moment Pearson Spearman Kendall * Nilai : -1 s/d +1

6 Regresi * Mampu membuat prediksi DV dari perubahan IV * Uji : - regresi sederhana - regresi majemuk * Persamaan : Y = a + b1x1 + b2x2.bixi * Tidak otomatis menunjukkan sebab akibat

7 Chi-squared (X 2 )test Used to test whether there is an interdependence between the row variable and the column variable. Observed number influenza vaccine placebo total Yes No Total

8 Observed and expected number influenza vaccine placebo total Yes (52,2) (47,8) No (187,8) (172,2) Total

9 Formula X 2 = (O E) 2 E The greater the difference between the observed and The greater the difference between the observed and expected numbers, the larger the value of X 2 and the less likely it is that the difference is due to chance

10 Continuity correction = Yt Yate s continuity it correction Is always advisable although it has most effect when the expected numbers are small When they are very small the alternative is Fischer s exact test t

11 Larger tables There is no continuity correction or exact test for contingency tables larger than 2X2. The chi-squared test is valid provided less than 20% of the expected numbers are under 5 and none is less than 1

12 Further methods for contingency tables Fischer s s exact test Comparison of two proportions paired case Mantel-Haenszel chi-squared test Association : phi, contingency coefficient, Cramer s V Risk

13 Fischer s Exact test Is used when the overall total of the tables is less than 20 or when it is between 20 and 40 and the smallest of the four expected values is less than 5. Thus the chi squared test is valid : -when the overall total is more than 40 regardless of the expected values -when the overall total is between 20 and 40 provided all the expected tdvalues are at tleast t5

14 Mc cnemar s schi-squared test Comparison of two proportions paired case Kato-Katz Pos Neg Pos Bell Neg 14 63

15 Incorrrect layout Result Bell Kato Total Total

16 Mantel-Haenszel chi-squared test When confounding is present, it is important to analyze the relevant subsets of the data separately. It is often useful, however, to apply a summary test which pools the evidence from the individual subsets, but which takes account of the confounding factor(s) The Mantel-Haenszel chi squared test is used for this purpose when the data consist of several 2 X 2 tables

17 Sex combined antibodies rural urban total yes no total X2= 0.012, p=0,913

18 antibodies rural urban total Male yes no total X2=5.73,,p=0.017 Female antibodies rural urban total yes no total X2=1 1.36, p=

19 vit A 1 inadekuat co 30 ug/dl * def Zn 1 cut off 65 ug/dl Crosstabs Crosstabulation Count vit A 1 inadekuat co 30 ug/dl Total ya tdk def Zn 1 cut off 65 ug/dl ya tdk Total Chi-Square Tests Pearson Chi-Square Continuity Correction Likelihood Ratio Fisher's Exact Test Linear-by-Linear Association N of Valid Cases a. b. a Computed only for a 2x2 table Value df Asymp. Sig. (2-sided) b cells (.0%) have expected count less than 5. The minimum expected count is Exact Sig. Exact Sig. (2-sided) (1-sided)

20 Crosstabs vit A 1 inadekuat co 30 ug/dl * def Zn 1 cut off 65 ug/dl Crosstabulation vit A 1 inadekuat co 30 ug/dl Total ya tdk Count Expected Count Count Expected Count Count Expected Count def Zn 1 cut off 65 ug/dl ya tdk Total

21 Chi-Square Tests Pearson Chi-Square Continuity a Correction Likelihood Ratio Fisher's Exact Test Linear-by-Linear Association N of Valid Cases Value a. Computed only for a 2x2 table b. df Asymp. Sig. (2-sided) b cells (.0%) have expected count less than 5. The minimum expected count is Exact Sig. Exact Sig. (2-sided) (1-sided)

22 Nominal by Nominal a. b. c. Directional Measures Asymp. Approx. Value Std. Error a Approx. T Sig. Lambda Symmetric vit A b. b inadekuat co b. b ug/dl Dependent def Zn 1 cut off 65 b b ug/dl Dependent Goodman vit A 1 and inadekuat Kruskal co c tau ug/dl Dependent def Zn 1 cut off 65 ug/dl c Dependent Not assuming the null hypothesis. Cannot be computed because the asymptotic standard error equals zero. Based on chi-square approximation

23 Nominal by Nominal N of Valid Cases Symmetric Measures Phi Cramer's V Contingency Coefficient Approx. Value Sig a. b. Not assuming the null hypothesis. Using the asymptotic standard error assuming the null hypothesis.

24 Risk Estimate Odds Ratio for vit A 1 inadekuat co 30 ug/dl (ya / tdk) For cohort def Zn 1 cut off 65 ug/dl = ya For cohort def Zn 1 cut off 65 ug/dl = tdk N of Valid Cases 95% Confidence Interval Value Lower Upper