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I need to draw a funnel plot for my meta-analysis, which is observational and aggregates prevalence rates of a certain medical condition. As far as I know, a funnel plot is a scatter plot of effect size measures against sample sizes. Therefore I have some difficulties in my study which I think does not have an effect size measure:

  1. I don't know if there is any effect size measures for prevalence of a single study? Each study reports a single prevalence, so I have a bunch of ratios (0-100%) only. Each study has only one single ratio, so there can be no "prevalence ratios" or "prevalence odds ratios".

  2. Can I plot the ratios (the prevalences) against sample sizes, instead of non-existent effect sizes against sample sizes?

  3. Can I calculate 95% CI for each ratio (each prevalence), and use it as the effect size? If so, does it help when the Y axis is already "Sample Size" and CI is directly affected by sample size?

  4. Do you have any other hints, in addition to the nice ones given here?

Many thanks.

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    $\begingroup$ The prevalence ratio is the effect measure in a prevalence study. Another possibile effect measure would be the prevalence odds ratio. This paper discusses the two measures. I've found a funnel plots with prevalences here (Fig. 3) and here. As the prevalence is a proportion, it might be possible to calculate the standard error if the sample size is given. $\endgroup$ Jun 25, 2013 at 14:33
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    $\begingroup$ Jup, for the POR, you need the prevalence rate of the cases and controls. $\endgroup$ Jun 25, 2013 at 14:54
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    $\begingroup$ Yes, I think so. $\endgroup$ Jun 25, 2013 at 15:01
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    $\begingroup$ Maybe this post can shed further light unto the issue. $\endgroup$ Jun 25, 2013 at 15:09
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    $\begingroup$ Update: I think I can calculate SE for prevalences too, thus SE is not non-existent. :) $\endgroup$
    – Vic
    Jun 26, 2013 at 7:45

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