Performing High-Powered Studies Efficiently With Sequential Analyses
Running studies with high statistical power, while effect size estimates in psychology are often inaccurate, leads to a practical challenge when designing an experiment. This challenge can be addressed by performing sequential analyses while the data collection is still in progress. At an interim analysis, data collection can be stopped whenever the results are convincing enough to conclude an effect is present, more data can be collected, or the study can be terminated whenever it is extremely unlikely the predicted effect will be observed if data collection would be continued. Such interim analyses can be performed while controlling the Type 1 error rate. Sequential analyses can greatly improve the efficiency with which data is collected. Additional flexibility is provided by adaptive designs where sample sizes are increased based on the observed effect size. The need for pre-registration, ways to prevent experimenter bias, and a comparison between Bayesian approaches and NHST are discussed. Sequential analyses, which are widely used in large scale medical trials, provide an efficient way to perform high-powered informative experiments. I hope this introduction will provide a practical primer that allows researchers to incorporate sequential analyses in their research.