Evidence Anxiety Series: Power: Episode 3

As a rule of thumb, if the researchers expect the treatment effect to be small, then the study has to be big, conversely, the smaller the study, the more likely it is that a small or rare effect is missed2. This relationship is the same regardless of the treatment applied, be it a surgical method, a behavior modification strategy, a drug, or a vaccine. Put even more simply, big studies have more power to det­­­ect differences. 1.  Jones SR, Carley S, Harrison M. An introduction to power and sample size estimation. Emerg Med J. 2003;20(5):453-458. doi:10.1136/emj.20.5.453 2.  Wilson Van Voorhis CR, Morgan BL. Understanding Power and Rules of Thumb for Determining Sample Sizes. Tutor Quant Methods Psychol. 2007;3(2):43-50. doi:10.20982/tqmp.03.2.p043 3.  Feinberg WE. Teaching the Type I and Type II Errors : The Judicial Process. Am Stat. 1971;25(3):30-32.

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