tips:hunter_schmidt_method
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tips:hunter_schmidt_method [2019/01/17 12:26] – external edit 127.0.0.1 | tips:hunter_schmidt_method [2022/08/03 11:32] (current) – Wolfgang Viechtbauer | ||
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- switch to the Hunter and Schmidt estimator to estimate the amount of heterogeneity. | - switch to the Hunter and Schmidt estimator to estimate the amount of heterogeneity. | ||
- | **A few details about step 1**: The large-sample equation for the sampling variance of a (Pearson product-moment) correlation coefficient is $$\text{Var}[r_i] = \frac{(1-\rho_i^2)^2}{n_i - 1}$$ (although one could also just divide by $n_i$, and not $n_i - 1$). Since this equation involves the (unknown) true correlation coefficient $\rho_i$, it is not usable in practice. One approach is to substitute $r_i$ for $\rho_i$, but the resulting estimator for $\text{Var}[r_i]$ can be very inaccurate, especially when the sample size of a study is small. Hunter and Schmidt instead suggest to calculate the sample-size weighted average of the correlation coefficients, | + | **A few details about step 1**: The large-sample equation for the sampling variance of a (Pearson product-moment) correlation coefficient is $$\text{Var}[r_i] = \frac{(1-\rho_i^2)^2}{n_i - 1}$$ (although one could also just divide by $n_i$, and not $n_i - 1$). Since this equation involves the (unknown) true correlation coefficient $\rho_i$, it is not usable in practice. One approach is to substitute $r_i$ for $\rho_i$, but the resulting estimator for $\text{Var}[r_i]$ can be very inaccurate, especially when the sample size of a study is small. Hunter and Schmidt instead suggest to calculate the sample-size weighted average of the correlation coefficients, |
Let's use the data from the meta-analysis by McDaniel et al. (1990) (on the validity of employment interviews) for such an analysis. The three adjustments described above are applied as follows: | Let's use the data from the meta-analysis by McDaniel et al. (1990) (on the validity of employment interviews) for such an analysis. The three adjustments described above are applied as follows: | ||
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H^2 (total variability / sampling variability): | H^2 (total variability / sampling variability): | ||
- | Test for Heterogeneity: | + | Test for Heterogeneity: |
Q(df = 159) = 647.6782, p-val < .0001 | Q(df = 159) = 647.6782, p-val < .0001 | ||
Model Results: | Model Results: | ||
- | estimate | + | estimate |
0.2005 | 0.2005 | ||
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H^2 (total variability / sampling variability): | H^2 (total variability / sampling variability): | ||
- | Test for Heterogeneity: | + | Test for Heterogeneity: |
Q(df = 159) = 643.4014, p-val < .0001 | Q(df = 159) = 643.4014, p-val < .0001 | ||
Model Results: | Model Results: | ||
- | estimate | + | estimate |
0.2680 | 0.2680 | ||
tips/hunter_schmidt_method.txt · Last modified: 2022/08/03 11:32 by Wolfgang Viechtbauer