I am reading the book: Terri D. Pigott. Advances in Meta-Analysis. Springer 2012. https://link.springer.com/book/10.1007/978-1-4614-2278-5

On page 10, there is a formula for standardized mean difference:

Source: Terri D. Pigott. Advances in Meta-Analysis. Springer 2012.

Is the only error there in the denominator of (2.10) and the line just after the formula?

How can one explain the formula (2.12)?

  • 1
    $\begingroup$ See the answers to stats.stackexchange.com/questions/1850/… I do not see an error in the section you quote, perhaps you need to specify exactly what it is? $\endgroup$
    – mdewey
    Apr 22, 2023 at 12:52
  • $\begingroup$ @mdewey Thank you for pointing out the Hedges' g. The error in (2.10) is that $s_p^2$ is variance, not standard deviation, as defined in (2.11). $\endgroup$
    – Viktor
    Apr 24, 2023 at 0:28

1 Answer 1


That's indeed an error. The denominator in (2.10) should be $s_p$, that is, the square-root of $s_p^2$, which is the pooled variance (which is given correctly by 2.11).


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