Paired Change SD Calculator
Recover the SD of within-person change from marginal SDs and an explicit correlation.
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Recover the SD of within-person change from two marginal SDs and their correlation. Use matching paired observations on the same scale. All default values are fictional.
Calculation results
SD of change: 7.4162
Assumptions and limits
SD(change) = √[SDbefore² + SDafter² − 2r SDbefore SDafter]. Correlation must be between −1 and 1. This is an algebraic identity for paired measurements, not an estimated correlation or a paired-test p-value. An assumed correlation must be justified and sensitivity-tested. Marginal summaries from different participant sets cannot supply a valid paired SD. Zero SD is a degenerate case, not proof of a precisely estimated population effect.
Cochrane: effect measures and calculations · Read the practical guide · Download blank worksheet (TXT)