Educational researchers often report effect sizes in standard deviation units (SD), but SD effects are hard to interpret. Effects are easier to interpret in percentile points, but conversion from SDs to percentile points involves a calculation that is not intuitive to educational stakeholders. We point out that, if the outcome variable is normally distributed, simply multiplying the SD effect by 37 usually gives an excellent approximation to the percentile-point effect. For students in the middle half of the distribution, the approximation is accurate to within 1 percentile point for effect sizes of up to 0.8 SD (or 29 to 30 percentile points).
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