Comparison of three Observational Analytical strategies Attribute Cohort Case-control Cross-sectional Classification of population Population free from condition or disease Cases with condition or disease with or without the characteristic, and controls Populations without- identification of condition or characteristic Sample represented Non-diseased Uncertain: the source population of the cases is unknown Survivors at a point or period in time Temporal sequence Prospective or Retrospective Retrospective Contemporary or retrospective Function Compares incidence rates in exposed and unexposed Compares prevalence of exposure among cases and controls Describes association between exposure and disease simultaneously

Comparison of three Observational Analytical strategies Attribute Cohort Case-control Cross-sectional Outcome Incidence of disease in exposed and unexposed Prevalence of exposure in cases and controls Prevalence of disease in exposed and unexposed Risk measure Relative risk, attributable risk Odds ratio (estimate of relative risk) Prevalence ratio (inexact estimate of relative risk); also odds ratio Evidence of causality Strong Needs more careful analysis Only suggestive Bias Easy to manage Needs more effort and sometimes very difficult to manage May be very difficult to manage