When one applies interim sample size reestimation based on nuisance parameter estimates (observe fraction of initial sample size, estimate nuisance parameter(s) based on the obtained data, reestimate sample size based on interim estimates of nuisance parameter(s), and observe remainder of patients (if necessary), do final analysis based on all the data), is this a case of double dipping/p-hacking? I think not, because you not test the hypothesis at interim, you only estimate the relevant parameters. Is this correct?
My read is that this wouldn't be "p-hacking" per se because you're not adjusting your analysis plan based on the hypothesis test. However, I would buy that this might inflate Type 1 error (the issue with p-hacking), so it might be useful to treat this as an instance of sequential analysis and correct for the potential inflation: http://daniellakens.blogspot.com/2014/06/data-peeking-without-p-hacking.html