The v1i and v2i values are the variances and covariances of the observed effects.
Asreml r users variance covariance matrix trial#
Since each trial provides effect size estimates for both outcomes, the estimates are correlated. So, the results from the various trials indicate that surgery is preferable for reducing the probing depth, while non-surgical treatment is preferable for increasing the attachment level. The contents of the dataset are:ġ 1 Pihlstrom et al. (I copy the dataset into dat, which is a bit shorter and therefore easier to type further below). The data are provided in Table I in the article and are stored in the dataset dat.berkey1998 that comes with the metafor package: The effect size measure used for this meta-analysis was the (raw) mean difference, calculated in such a way that positive values indicate that surgery was more effective than non-surgical treatment in decreasing the probing depth and increasing the attachment level. Reported outcomes include the change in probing depth (PD) and attachment level (AL) one year after the treatment. The use of the model is illustrated with results from 5 trials comparing surgical and non-surgical treatments for medium-severity periodontal disease. (1998) describe a meta-analytic multivariate model for the analysis of multiple correlated outcomes.
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