on statistical testing

Reviewer asserts “the appropriate test for these particular data is a two-way ANOVA, (but be careful when analyzing proportions.  The data should be arc-sine transformed to minimize deviations from the assumption of normality).

ANOVA has long been used to classify treating a system in two different experimental conditions (like different temperatures).  There are 3 key assumptions:

  • the cases are independent (I believe this is the same sort of independence when we assert that different embryos are independent random draws from the underlying population distribution).
  • the data are normal.  (Our experimental data is not described by a normal distribution.  A simple, biophysical model predicts that the data should not be normally distributed).
  • homoscadsticity: the data has constant variance. (this is certainly not the case, and it is in fact one of the conclusions of our paper).
  • required for unit-treatment additivity: observed response = unit response + treatment effect.   There is no a priori reason to believe the effect of temperature on failure rate should be additive.
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