What is the ‘correct’ way to compare the effect of a drug in different conditions? For example, if I have conditions a, b, c and d, where there are different numbers of ‘control’ and ‘drug’ cells in each condition and a single parameter has been measured in control and drug-treated cell (different cells).
Of course I can easily calculate the % effect of the drug for each condition, and determine whether the effect is significant (eg unpaired Student’s t-test or non-parametric equivalent). However, how do I appropriately determine whether the effect of the drug is different in each condition?
Comparing p-values across groups is not valid (e.g. Gelman, A., & Stern, H. (2006). The Difference Between “Significant” and ‘Not Significant’ is not Itself Statistically Significant. The American Statistician, 60(4), 328–331 or Nieuwenhuis, S., Forstmann, B. U., & Wagenmakers, E.-J. (2011). Erroneous analyses of interactions in neuroscience: a problem of significance. Nature Neuroscience, 14(9), 1105–1107).