This may seem like a ridiculous question, but it's bugging me and no text book or paper I've read has answered it. I am looking into research on effect sizes and their use in research. I see a lot of mention of Cohen's D and F2 and the "small", "medium" and "large" effect sizes. Can someone explain (with an example) why a researcher would choose a "medium" effect size for example? I'm just not seeing any justifications and I know it isn't just an arbitrary decision.
Effect Sizes
- Thread starter chadwae
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- Tags effect size research statistics
Welll... Cohen's original effect sizes were based on his rough experience of what was most common in psychology. So hypothesising a "medium" effect size is like hypothesising a typical, expected effect size (although in reality Cohen's medium effect size is a bit higher than the average in psychology - see Richard et al.). But most likely the researcher just can't be bothered coming up with a more specific hypothesis, and is going with convention.