title: You cannot exclude the explanation you have not considered.
authors.affiliation: Epidemiology Unit, Tuberculosis Research Centre, Chetpet, Madras, India.
authors.forename: M
authors.initials: M
authors.lastname: Datta
mesh_terms: D016022:Case-Control Studies; D015984:Causality; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D006801:Humans; D015999:Multivariate Analysis; D011897:Random Allocation; D012106:Research; D012107:Research Design; D012307:Risk Factors