Sample size and power calculationsGuideline in PDF

Aim

Most grant applications require a sample size calculation. This is associated with the level of statistical power required for the tests, which will be calculated on future study data. The aim of this guideline is to describe how this information can be produced in an efficient and proper way.

Description

There are numerous formulas for calculating sample size and/or power [Cohen, 1988]. The differences correspond to differences in study design.

From a statistical point of view, a lot of power calculations should come with critical notes. This is due to the fact that it is often difficult to provide a true estimate of the statistics required for each formula.
On the other hand, a sample size calculation is required for most grant applications to allow people to complete the necessary parameter values one way or the other.
An overview of calculation methods is provided on: http://www.math.uiowa.edu/~rlenth/Power/

Consult one of our biostatisticians for assistence

Cohen J. Statistical power analyses for the behavioral sciences. Hillsdale, New Jersey: Lawrence Erlbaum, 2nd edn., 1988.

V1.1: 1 Jan 2010: Translation into English and updated.
V1.0: 1 May 2005: Minor textual amendments.

1. Has a power calculation been undertaken for each of your primary outcome measures? If so, has the measurement level of the outcomes been taken into consideration? If not, why not?
2. In the event of equivalence research, did you take the particular requirements imposed on the power calculations by this design into account?
3. Did the analysis investigate whether the power calculations in the protocol are based on realistic assumptions? If not, did you record this (in articles and reports)?
4. If the actual sample size was smaller than that calculated in advance, how was this dealt with in the analysis?