ABSTRACT
The association between an exposure of interest (risk factor) and a disease may be confounded by the action of other separate factors as well as by interactions between risk factors exerting an impact. Crude measures of effect may be misleading in such situations. Levels of the potential confounding factor could be estimated using stratified analysis. Uniformity of the stratum-specific effect estimates can be assessed by performing chi-square tests for heterogeneity. If the effect is uniform across strata, we can calculate a pooled adjusted summary estimate of the effect using the Mantel-Haenzel (M-H) method. Confidence intervals for the adjusted estimate and the M-H chi-square test are calculated to assess the significance. If the effect is not uniform (presence of interaction), we report stratum-specific estimates, confidence intervals and chi-square for each estimate. In the present paper, assessment of the level of confounding and interaction between risk factors are illustrated using a case-control study of lung cancer conducted at the Regional Cancer Centre, Trivandrum.