PubMed ID:
16315649
Public Release Type:
Journal
Publication Year: 2005
Affiliation: The Biostatistics Center, Department of Epidemiology and Biostatistics, The George Washington University, Rockville, Maryland 20852, USA. jml@biostat.bsc.gwu.edu
DOI:
https://doi.org/10.1191/1740774505cn115oa
Authors:
Lachin JM
Studies:
Diabetes Control and Complications Trial
Expressions to determine the sample size N needed to provide power 1-beta to detect a difference between groups, say delta, involve other nuisance parameters, such as the variance of the observations for a test or means, or the control group probability for a test of proportions or the control group hazard rate for a logrank test of event-times. Designs where N is fixed are called maximum N or duration designs because the sample size and required duration of the study can be fixed, or estimated. However, such designs are expected, but not guaranteed, to provide the desired level of power to detect the specified difference delta at the study end because the true or estimated values of the nuisance parameters are unknown. Thus, the actual information to be accrued and the associated level of power are random variables with sample variation.