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Table 3 Absolute frequencies, outcome prevalences, exposure prevalences, crude and pooled prevalence ratio (PR) estimates, and relative confounding for the analysis of the original data using asthma as the outcome, maternal smoking as the risk factor and social class as confounder (situation 2 original).

From: Alternatives for logistic regression in cross-sectional studies: an empirical comparison of models that directly estimate the prevalence ratio

First stratum: High social class
  Asthma No All  
  N Prev. N N Exp. prev. = 26.6%
Mother smokes 37 25.7% 107 144 PR = 1.19
No 86 21.6% 312 398 M-H weight = 22.85
All 123 22.7% 419 542  
Second stratum: Low social class
  Asthma No All  
  N Prev. N N Exp. prev. = 43.3%
Mother smokes 122 42.8% 163 285 PR = 1.24
No 129 34.6% 244 373 M-H weight = 55.87
All 251 38.1% 407 658  
Combined strata: High and low social class
  Asthma   No All Exp. prev. = 35.8%
  N Prev. N N PR (crude) = 1.33
Mother smokes 159 37.1% 270 429 PR (M-H) = 1.22
No 215 27.9% 556 771 Confounding = -7.9%
All 374 31.2% 826 1200 P-value(het)*= 0.8
  1. * P-value for testing heterogeneity of the prevalence ratios across strata.