Dear Michael and other readers,
Please see below for my answers to your questions about my data.
On 07/06/2013 02:56 PM, Michael Dewey wrote:
[..]
Because everything was randomized, I can only calculate the total
number of times a certain response was used under each type of trial.
There is no pairing of trials under two treatments, so I am forced to
use the marginal totals from your table.
But presumably you could calculate some statistic suitable for
summarising the relevant features here? Difference in proportions, odds
ratio, ...
Using the totals, it is indeed easy to calculate the difference in
proportions or odds ratio based on these totals. However, I am not sure
how I should calculate a study-level statistic suitable for
meta-analysis on the basis of these participant-level proportion
differences.
So, for instance, I have the following table;
pp proportion_difference
1 0.1
2 0.05
3 0.08
4 0.02
..
N ..
Can I just calculate the mean and standard deviation of these proportion
differences -- mean(proportion_difference) and sd(proportion_difference)
-- and use these for meta-analysis? If yes, what escalc measure should I
use?
[..]
One alternative that I have tried over the last few days, is to use
the b parameter of interest and it's corresponding standard error from
the lme4 regression output that I use to analyse the individual
experiments. Then, I use rma(yi, sei) to do a meta-analysis on these
parameters. I am not sure this is correct though, since it takes into
account between-subjects variance (through a random effect for
subject), and it is sensitive to the covariates/moderators I include
in the models that I get the b parameters from.
So you end up with 5 values of b? The fact that they adjust for
different moderators does not seem an issue to me, indeed it could be
argued to be an advantage of the meta-analytic approach here.
OK, thank you for your comment on this one. I think the results of a
meta-analysis using these 5 b values are indeed more or less sensible,
which is encouraging. I think I will go this way if it turns out I
cannot find a simpler approach, as a simpler approach would be easier to
sell to potential reviewers.
[..
I think we are all assuming you have different participants in each
experiment but I thought I would raise that as a question.
You are right in assuming this, I have different participants in all 5
experiments.
Thanks all for the help so far, your suggestions are highly appreciated!
Regards,
Marc
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