Description

The function computes predicted values, corresponding standard errors, confidence intervals, and (approximate) credibility/prediction intervals for objects of class "rma".

Usage

Arguments

Details

For a fixed-effects model, predict(object) returns the estimated (average) outcome in the set of studies included in the meta-analysis. This is the same as the estimated intercept in the fixed-effects model.

For a random-effects model, predict(object) returns the estimated (average) outcome in the hypothetical population of studies from which the set of studies included in the meta-analysis are assumed to be a random selection. This is the same as the estimated intercept in the random-effects model.

For models including one or more moderators, predict(object) returns the estimated (average) outcomes for values of the moderator(s) equal to those of the k studies included in the meta-analysis (i.e., the fitted values for the k studies).

For models including q moderator variables, new moderator values for k_new new studies can be specified by setting newmods equal to an k_new x q matrix with the corresponding new moderator values. If the original model includes an intercept, then it should not be explicitly specified under newmods, as it will be added by default (unless one sets intercept=FALSE). Also, any factors in the original model get turned into the appropriate contrast variables within the rma function, so that newmods should actually include the values for the contrast variables. Examples are shown below.

For random/mixed-effects models, an approximate credibility/credible or prediction interval is also calculated (Raudenbush, 2009; Riley et al., 2011). The interval estimates where level % of the true outcomes fall in the hypothetical population of studies. Note that this interval is calculated under the assumption that the value of τ² is known (and not estimated). A method for calculating a credibility/prediction interval that accounts for the uncertainty in the estimate of τ² may be implemented in the future.

For random-effects models of class "rma.mv" (see rma.mv) with multiple τ² values (i.e., when the random argument includes a ~ inner | outer term and struct="HCS", struct="HAR", or struct="UN"), the function will provide credibility/prediction intervals for each level of the inner factor (since the credibility/prediction intervals differ depending on the τ² value). Alternatively, one can use the tau2.levels argument to specify for which level(s) the credibility/prediction interval should be provided.

If the model includes a second ~ inner | outer term with multiple γ² values, credibility/prediction intervals for each combination of levels of the inner factors will be provided. Alternatively, one can use the tau2.levels and gamma2.levels arguments to specify for which level combination(s) the credibility/prediction interval should be provided.

When using the newmods argument for mixed-effects models of class "rma.mv" with multiple τ² (and multiple γ²) values, one must use the tau2.levels (and gamma2.levels) argument to specify the levels of the inner factor(s) (i.e., a vector of length k_new) to obtain the appropriate credibility/prediction interval(s).

Value

An object of class "list.rma". The object is a list containing the following components:

If vcov=TRUE, then the returned object is a list with the first element equal to the one as described above and the second element equal to the variance-covariance matrix of the predicted values.

The "list.rma" object is formatted and printed with print.list.rma.

Note

The predicted values are based only on the fixed effects of the model. Best linear unbiased predictions (BLUPs) that combine the fitted values based on the fixed effects and the estimated contributions of the random effects can be obtained with blup.rma.uni (currently only for objects of class "rma.uni").

When using the transf option, the transformation is applied to the predicted values and the corresponding interval bounds. The standard errors are then set equal to NA and are omitted from the printed output. Also, vcov=TRUE is ignored when using the transf option.

Confidence and credibility/prediction intervals are calculated based on the critical values from a standard normal distribution (i.e., +- 1.96 for level=95). When the model was fitted with the Knapp and Hartung (2003) method (i.e., test="knha" in the rma.uni function) or with test="t" in the rma.glmm and rma.mv functions, then the t-distribution with k-p degrees of freedom is used.

Author(s)

Wolfgang Viechtbauer wvb@metafor-project.org http://www.metafor-project.org/

References

Hedges, L. V., & Olkin, I. (1985). Statistical methods for meta-analysis. San Diego, CA: Academic Press.

Raudenbush, S. W. (2009). Analyzing effect sizes: Random effects models. In H. Cooper, L. V. Hedges, & J. C. Valentine (Eds.), The handbook of research synthesis and meta-analysis (2nd ed., pp. 295–315). New York: Russell Sage Foundation.

Riley, R. D., Higgins, J. P. T., & Deeks, J. J. (2011). Interpretation of random effects meta-analyses. British Medical Journal, 342, d549.

Viechtbauer, W. (2010). Conducting meta-analyses in R with the metafor package. Journal of Statistical Software, 36(3), 1–48. https://www.jstatsoft.org/v036/i03.

See Also

fitted.rma, blup.rma.uni

Examples