4

For simplicity let us assume there are two groups although the issues are the same for multiple groups. The choices are (a) to run an analysis on each group separately (b) to run an analysis on the whole data-set with a two-level factor as a moderator. The advantage of option (b) is that you have more data and hence your estimate of $\tau^2$ will be more ...


3

Your setting describes a pretest-posttest-control group design, hence you should not use a (standardized) mean difference measure but a (standardized) measure of mean change. You can read a broad overview in Chapter 6 of the Cochrane Handbook and in Viechtbauer's documentation on conducting meta-analysis in R with the metafor package. What is mean change? ...


2

If you include studies with different ways of estimating the presence of an event then you are making the assumption that they come to the same ting. So for example if the adverse event is pain at the injection site and some just ask whether the patient experienced it while other rate it on a four point scale from 0 to 3 and then choose 2 and 3 as present ...


2

The exact conversion of a point-biserial correlation coefficient (i.e., the correlation between a binary and a numeric/quantitative variable) to a Cohen's d value is: $$d = \frac{r \sqrt{h}}{\sqrt{1-r^2}},$$ where $h = m/n_0 + m/n_1$, $m = n_0 + n_1 - 2$, and $n_0$ and $n_1$ are the number of 0's and 1's respectively. Here is some R code to demonstrate that ...


1

If you have the individual data then you can fit a single model to the whole dataset. This is usually called individual participant data meta-analysis if you do it with many different data sources. Sometimes also called one-step IPD to distinguish it from the other option you mention, to analyse each set separately then meta-analyse them, known as two-step ...


1

Q1 - if you show an effect of the moderator then there is no overall effect. It would be like estimating the average height of humans when you have shown that men are taller than women. Q2 - the coefficient for crop applies irrespective of soil level and vice versa unless you fit an interaction. Q3 - with the sort of numbers you quote I suspect if you try to ...


1

It depends whether the data obtained using different methodologies can be statistically compared. Normally in a MA you first show the results overall and then you run a sensitivity analysis e.g. stratified analysis.


1

There definitely should be a multiple comparison correction. Meta-analyses are...generally not of the highest quality, with regards to statistical soundness.


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