1 Observational Studies 1 2 Randomized Experiments 19 3 Overt Bias in Observational Studies 71 4 Sensitivity to Hidden Bias 105 5 Models for Treatment Effects 171 6 Known Effects 205 7 Multiple Reference Groups in Case-Referent Studies 231 8 Multiple Control Groups 253 9 Coherence and Focused Hypotheses 277 10 Constructing Matched Sets and Strata 295 11 Planning an Observational Study 333 12 Some Strategic Issues 367 Index 370