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Have you ever asked yourself, “how should I approach the classic pre-post analysis?”

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Well, maybe not, but this comes up all the time. An investigator wants to assess the effect of an intervention on a outcome. Study participants are randomized either to receive the intervention (could be a new drug, new protocol, behavioral intervention, whatever) or treatment as usual. For each participant, the outcome measure is recorded at baseline – this is the pre in pre/post analysis. The intervention is delivered (or not, in the case of the control group), some time passes, and the outcome is measured a second time. This is our post. The question is, how should we analyze this study to draw conclusions about the intervention’s effect on the outcome? There are at least three possible ways to approach this. (1) Ignore the pre outcome measure and just compare the average post scores of the two groups. (2) Calculate…
Original Post: Have you ever asked yourself, “how should I approach the classic pre-post analysis?”