Application of statistical power analysis - How to determine the right sample size in human health, comfort and productivity research

The minimum size of subjects required for the research on human health, thermal comfort and productivity is a frequently asked question. In this paper the idea of power analysis, which helps to determine required sample size as well as to interpret research results, is introduced in order to promote good practice of power analysis in the context of human and building environment relationship research. How to calculate effect size from published article or experimental data is presented with plenty of examples. The effect sizes of several physiological and psychological measurements indicating the effect of indoor environment quality on human health, thermal comfort and productivity are presented, which could be worked as references when researchers planning their own studies. How to determine required sample size when planning a study and how to interpret the research results with power analysis are also illustrated step by step with samples. Finally how to make decisions when evaluating the study results is summarized. It is expected that these examples and the summary could help researchers to better apply power analysis in indoor environment quality (IEQ) studies. Some statistical terms used in this paper, such as power analysis, effect size, and t-test, etc., are explained in detail in the Appendix. (C) 2009 Elsevier Ltd. All rights reserved.