Related link :
Sample Size Introduction and Explanation Page
Sample Size for Unpaired Differences Tables Page
Unpaired Difference Explanation Page
Program
Data Input
References
Two Groups
Multiple (>2) Groups
Data Input for Sample Size is a table of 4 columns
 Each row contains data from a separate study
 Col 1 = Probability of Type I Error α
 Col 2 = Power (1  β)
 Col 3 = Difference Between the Two Means to be Detected
 Col 4 = Expected Within Group Standard Deviation
Data Input for Power Estimation is a table of 6 columns
 Each row contains data from a separate study
 Col 1 = probability of Type I error (α)
 Col 2 = Differences between group means observed
 Col 3 = sample size Group 1 used
 Col 4 = Standard Deviation of Group 1 observed
 Col 5 = sample size Group 2 used
 Col 6 = Standard Deviation of Group 2 observed
Data Input for Confidence Interval Estimation is a table of 5 columns
 Each row contains data from a separate study
 Col 1 = Percent confidence (usually 95 or 99)
 Col 2 = sample size group 1
 Col 3 = Standard Deviation group 1
 Col 4 = sample size group 2
 Col 5 = Standard Deviation group 2
Data Input for Pilot Study is for a single plan, a single column with 4 rows
 Row 1 : Percent confidence required, usually 95 or 99
 Row 2 : within Group or pupulation Standard Deviation
 Row 3 : Sample size interval for tabulation of changing width of the confidence interval. This is usually
established by trial and error, starting at about 5
 Row 4 : Maximum sample size (per Alpha) for tabulation of changing width of the confidence interval. This is usually
established by trial and error. For most clinical studies however, the sample size is between 10 and 200,
and this range can be used as starting levels
Sample Size is a table of 5 columns
 Each row contains data from a separate study
 Col 1 = Probability of Type I Error (α)
 Col 2 = Power (1β)
 Col 3 = The Number of Groups in the study
 Col 4 = Maximum Difference Between Any Two Groups to be Detected
 Col 5 = Expected Residual Standard Deviation (sqrt(residual mean sum square))
Power Estimation is a table of 5 columns
 Each row contains data from a separate study
 Col 1 = Probability of Type I Error α
 Col 2 = Averaged numbers per group used
 Col 3 = The Number of Groups in the study
 Col 4 = Maximum Difference Between Any Two Groups observed
 Col 5 = Residual Standard Deviation (sqrt(residual mean sum square)) from data
Pilot is for a single plan, a single column with 5 rows
 Row 1 : Probability of Type I Error usually 0.05
 Row 2 : The Number of Groups in the study
 Row 3 : Largest Difference Between Groups to be detected
 Row 4 : Expected within group or population Standard Deviation
 Row 5 : Sample size interval for tabulation of changing values of Power. This is usually
established by trial and error, starting at about 5
 Row 6 : Maximum sample size or tabulation of changing width of the confidence interval. This is usually
established by trial and error. For most clinical studies however, the sample size is between 10 and 200,
and this range can be used as starting levels
Two Groups
Armitage P (1980) Statistics in Medical Research. Blackwell Scientific Publication, Oxford. ISBN 0 632 05430 1 p.120
Machin D, Campbell M, Fayers, P, Pinol A (1997) Sample Size Tables for Clinical
Studies. Second Ed. Blackwell Science IBSN 0865428700 p. 2425
Multiple (>2) Groups
Cohen J (1988) Statistical power analysis for the behavioral sciences. Second edition.
Lawrence Erlbaum Associates, Pubishers. London. ISBN 0805802835 p. 276279, p. 550
