faq
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faq [2020/03/16 20:05] – Wolfgang Viechtbauer | faq [2020/06/26 06:56] – Wolfgang Viechtbauer | ||
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??? How are $I^2$ and $H^2$ computed in the metafor package? | ??? How are $I^2$ and $H^2$ computed in the metafor package? | ||
- | !!! For random-effects models, the $I^2$ statistic is computed with $$I^2 = 100\% \times \frac{\hat{\tau}^2}{\hat{\tau}^2 + \tilde{v}}, | + | !!! For random-effects models, the $I^2$ statistic is computed with $$I^2 = 100\% \times \frac{\hat{\tau}^2}{\hat{\tau}^2 + \tilde{v}}, |
Therefore, depending on the estimator of $\tau^2$ used, the values of $I^2$ and $H^2$ will change. For random-effects models, $I^2$ and $H^2$ are often computed in practice with $I^2 = 100\% \times (Q-(k-1))/ | Therefore, depending on the estimator of $\tau^2$ used, the values of $I^2$ and $H^2$ will change. For random-effects models, $I^2$ and $H^2$ are often computed in practice with $I^2 = 100\% \times (Q-(k-1))/ | ||
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!!! The pseudo $R^2$ statistic (Raudenbush, | !!! The pseudo $R^2$ statistic (Raudenbush, | ||
- | ??? For random-effects models fitted with the rma() function, how is the credibility/ | + | ??? For random-effects models fitted with the rma() function, how is the prediction interval computed by the predict() function? |
!!! By default, the interval is computed with $$\hat{\mu} \pm z_{1-\alpha/ | !!! By default, the interval is computed with $$\hat{\mu} \pm z_{1-\alpha/ | ||
- | Note that this differs from Riley et al. (2001), who suggest to use a t-distribution with $k-2$ degrees of freedom for constructing the interval. Neither a normal, nor a t-distribution with $k-1$ or $k-2$ degrees of freedom is correct; all of these are approximations. The computations in metafor are done in the way described above, so that the credibility/ | + | Note that this differs |
??? How is the Freeman-Tukey transformation of proportions and incidence rates computed? | ??? How is the Freeman-Tukey transformation of proportions and incidence rates computed? |
faq.txt · Last modified: 2023/01/24 07:56 by Wolfgang Viechtbauer