The Power Analysis method of estimating sample size depends on a mathematical relationship between the following six variables.
Variability of the material


Effect size of clinical or biological importance


Significance level


Power


Sidedness of the test


Sample size

Putting it together

The two sample case

The two sample case with binary outcomes (e.g. percentages)




























































More complex situations

The ILAR web site http://dels.nas.edu provides extensive information on all aspectes of laboratory animal science. Full text of an excellent article on power analysis is given in
http://dels.nas.edu/ilar_n/ilarjournal/43_4/v4304Dell.shtml
Additional web sites dealing with power calculations are:
http://davidmlane.com/hyperstat/power.html