Interim analyses without any stopping rules I've got some questions about interim analysis rules.
Do I need to make alpha/beta corrections in the following situation:


*

*One interim analysis is planned in the study  

*The interim analysis is needed for sample size re-estimation only.

*I don't need to stop the study early

*$H_o$ or $H_a$ are not tested at the interim analysis

*Need to estimate means and standard deviations and re-estimate sample size.


Should I use any alpha/beta corrections? Could you please explain the point or give some links?
 A: I assume that this is some form of randomized controlled trial and that there is no chance that the unblinded group/data monitoring committee would decide to reject $H_0$ after seeing the interim results (some authors argue to always add an adjustment to give them a criterion and to always pay some penalty for all interim analyses). The main question would be the exact nature of the sample size re-estimation. There are forms of blinded sample size re-estimation that do not need an adjusted in order to control the type I error rate, but unblinded sample size re-estimation e.g. when it takes into account the group means typically results in a need for adjustment in order to control the type I error rate.
One methodology that allows to adjust for this would be adaptive design methods (e.g. p-value combination approaches) and there is an extensive literature on this. A good starting point for reading up on the topic could be: Vandemeulebroecke, Marc. "Group sequential and adaptive designs–a review of basic concepts and points of discussion." Biometrical Journal 50.4 (2008): 541-557.
Note that you will not necessarily have e.g. unbiased estimates, even if your analysis approach controls the type I error rate.
