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There are two groups of patients, say, young and old, and we want to determine whether these two groups of patients react differently to our treatment. Let $X$ be a continuous dependent variable, say, blood pressure which will be measured twice for every patient: once before the treatment and once after. An average change of $X$ after the treatment will be calculated for the first and second group, say, values $A_1$ and $A_2$, respectively.

  1. How can we check whether there is a statistically significant difference between $A_1$ and $A_2$?
  2. How can we conduct power analysis to estimate the size of the groups if we know only the measurement error of $X$ and the expected difference between $A_1$ and $A_2$?
  3. Questions 1 and 2 is for the scenario when we measure not absolute, but relative changes in variable $X$.
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  • $\begingroup$ Is A1 and A2 different treatments? If so, that would mean both groups are “treated” in the second time period? $\endgroup$ – Thomas Bilach Mar 30 at 6:31
  • $\begingroup$ Thank you for your question! I just edited my question for clarity. $\endgroup$ – Mark Mar 30 at 16:09

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