BMJ  2003;326:1083-1084 (17 May), doi:10.1136/bmj.326.7398.1083

Education and debate

Effect of regression to the mean on decision making in health care

¹ York Trials Unit, Department of Health Sciences, University of York, York YO10 5DD

Knowledge of regression to the mean can help with everything from interpreting test results to improving your career prospects. All healthcare professionals should be aware of its implications

The first 150 words of the full text of this article appear below.

Regression to the mean is a widespread statistical phenomenon with potentially serious implications for health care. It can result in wrongly concluding that an effect is due to treatment when it is due to chance. Ignorance of the problem will lead to errors in decision making. We discuss the importance of the issue and its effects on many common clinical, public health, and managerial decisions.

Regression to the mean occurs whenever a nonrandom sample is selected from a population and two imperfectly correlated variables are measured, such as two consecutive blood pressure measurements. The less correlated the two variables, the larger the effect of regression to the mean. Also, the more extreme the value from the population mean, the more room there is to regress to the mean. It occurs whenever a group is selected with extreme values for one variable and another variable is then measured.^{1 2}

Francis Galton documented . . . [Full text of this article]

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