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75 lines
2.7 KiB
Plaintext
75 lines
2.7 KiB
Plaintext
7 months ago
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help for ^galbr^ (STB-41: sbe20; STB-56: sbe20.1)
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.-
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Assessing heterogeneity in meta-analysis: the Galbraith plot
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------------------------------------------------------------
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^galbr^ theta setheta [^if^ exp] [^in^ range] [, ^id(^strvar^)^ graph_options]
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Description
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-----------
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^galbr^ provides a graphical display to get a visual impression of the amount of
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heterogeneity from a meta-analysis. For each trial, the z statistic
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^theta/setheta^ is plotted against the reciprocal standard error ^1/setheta^.
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The (unweighted) regression line constrained through the origin, with its 95%
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confidence interval, has a slope equal to the overall log rate ratio,
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or log odds ratio, or log hazard ratio in a fixed effects meta-analysis.
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The position of each trial on the horizontal axis gives an indication of the
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weight allocated to it in a meta-analysis. The position on the vertical axis
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gives the contribution of each trial to the Q statistic for heterogeneity.
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In the absence of heterogeneity we could expect all the points to lie within
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the confidence bounds (positioned 2 units over and below the regression line).
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^theta^ is the effect estimated from the individual study, and ^setheta^ is
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its standard error. For example theta might be a difference in means, a
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log rate ratio, a log odds ratio or a log hazard ratio.
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If you have a dataset which contains data for all studies, then the @byvar@
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command can be used to derive the effect estimates and standard errors for the
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individual studies. For example:
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. ^sort study^
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. ^byvar study, coef(group) se(group) generate:^
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. ^quietly poisson cases group, e(pyrs)^
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. ^sort study^
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. ^qui by study: keep if _n==1^
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. ^rename _C_1 logrr^
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. ^rename _S_1 se^
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. ^galbr logrr se, id(study) yline(0)^
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Alternatively, the @collapse@ command may be useful.
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Options
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-------
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Graph options are allowed, but ^ylabel()^, ^yscale()^, ^xscale()^, ^symbol()^
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are not suggested.
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^id(^labelvar^)^ supplied any variable, which is used to label the studies.
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If the data contains a labeled numeric variable, it can also be used.
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^yline(^0^)^ is a useful to check it with the direction and intensity of the
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overall effect estimated in a fixed effects meta-analysis by the slope
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of the (unweighted) regression line constrained through the origin.
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Author
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-------
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Aurelio Tobias
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Universidad Miguel Hernandez, Alicante, Spain
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email: bledatobias@@ctv.es
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Also see
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--------
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STB: STB-41 sbe20, STB-38 sbe16
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On-line: help for @graph@, @byvar@, @collapse@, @for@, @meta@ (if installed),
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@metareg@ (if installed), @metabias@ (if installed), @metacum@ (if
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installed), @metainf@ (if installed)
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