leading Schou & Marschner to conclude that "early stopping of clinical trials is not a substantive source of bias in meta-analyses". The meaning of p-values in sequential analyses also changes, because when using sequential analyses, more than one analysis is performed, and the typical definition of a p-value as the data “at least as extreme” as is observed needs to be redefined. One solution is to order the p-values of a series of sequential tests based on the time of stopping and how high the test statistic was at a given look, which is known as stagewise ordering, first proposed by Armitage. See also Optimal stopping Sequential estimation Sequential probability ratio test CUSUM Notes References Bartroff, J., Lai T.L., and Shih, M.-C. (2013) Sequential Experimentation in Clinical Trials: Design and Analysis. Springer. Bakeman, R., Gottman, J.M., (1997) Observing Interaction: An Introduction to Sequential Analysis, Cambridge: Cambridge University Press Jennison, C. and Turnbull, B.W (2000) Group Sequential Methods With Applications to Clinical Trials. Chapman & Hall/CRC. Whitehead, J. (1997). The Design and Analysis of Sequential Clinical Trials, 2nd Edition. John Wiley & Sons. External links R Package: Wald's Sequential Probability Ratio Test by OnlineMarketr.com Software for conducting sequential analysis and applications of sequential analysis in the study of group interaction in computer-mediated communication by Dr. Allan Jeong at Florida State University Commercial PASS Sample Size Software includes features for the setup of group sequential designs. Statistical hypothesis testing Design of experiments Sequential methods