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The use of information in sequential monitoring of clinical trials is described. Technically defined as the inverse of the variance of some estimate, the information in a trial depends on the type of data collected on the patients. We examine three common situations: comparison of two means, comparison of two survival curves, and comparison of two populations slopes from repeated measures data. In each case we discuss how to proceed when the information available at the planned end of the trial, the total information, is unknown. The amount of information at a given interim analysis divided by the total information is the information fraction. Some natural estimates of the information fraction and their relationships to calender time are presented. The concept of total information can also be useful for the design of trials collecting repeated measures data.
Lan et al. (Sat,) studied this question.