STAB22H3 Lecture Notes - Lecture 5: Stratified Sampling, Random Assignment, Statistical Inference
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Definition: available data are data that were produced in the past for some other purpose but that may help answer a present question. However, often we need to produce data to answer specific questions. In an observational study we observe individuals and measure variables of interest but do not attempt to influence the responses. In an experiment we deliberately impose some treatment on individuals and we observe their responses. The best way to see the effects of a change is to do an intervention where we actually impose the change. Example: a study of child care enrolled 1364 infants in 1991 and planned to follow them through their sixth year in school. Parents made all child care decisions and the study did not attempt to influence them. The study cannot prove whether spending more time in child care causes children to have more problem behaviors.
