PHI 31 Lecture Notes - Lecture 19: Random Assignment
Document Summary
Subjects self-select (choose for themselves whether to belong to the treatment (x) or control (k) group) or are selected by nature : +c is already present when sampling is performed. Sampling is from each subpopulation of the actual population, not as if from hypothetical x, k populations by random assignment into treatment, control groups: +e is not present. Prospective means you follow forward in time and wait for +e to occur: contrast pro with red. In red, neither +c nor +e is present at the start. In pro, +c is present, but not +e: residual states problem for pro. In red, the whole residual state is randomized by random assignment. In pro, those self-selecting into the +c group may also be different in residual state from -c group in other ways. Ex: smoker (+c) tend to be coffee drinkers (+d) Pro: ways to control residual state (s)
