Suppose one would like to test some new hypothesis, for which there are no previous data available. To estimate the needed sample size, one should do a power analysis. Since there are no previous data available, the power analysis can only be carried out by conducting a pilot study first. How does one choose the sample size for a pilot study?
The field is neuroscience, where sample sizes are generally small due to financial and other constraints (cost per measured subject is easily in the thousands).
If I'd like to compare two groups, would a pilot study with 4+4 participants be enough to run a power analysis? How does the sample size of the pilot study affect the reliability of the power analysis?
Are the there any techniques (e.g. bootstrap?) that I could use to improve the power analysis?