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help for ^metatrim^ (Stata 6; version 1.0.5)
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Nonparametric "trim and fill" analysis of publication bias in meta-analysis
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^metatrim^ { theta { se_theta | var_theta } | exp(theta) ll ul [cl] }
[ ^if^ exp ] [ ^in^ range ] [^,^ { ^v^ar | ^ci^ } ^re^ffect ^pr^int
^est^imator^(^{ ^r^un | ^l^inear | ^q^uadratic }^) ef^orm ^f^unnel
^l^evel^(^#^) g^raph ^id^var^(^var^) sa^ve^(^filename [^, replace^]^)^
^flip^ ^mixed^ graph_options ]
where { a | b |...} means choose one and only one of {a, b, ...}.
Description
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^metatrim^ performs the Duval and Tweedie nonparametric "trim and fill" method
of accounting for publication bias in meta-analysis. The method, a rank-based
data augmentation technique, formalizes the use of funnel plots, estimates
the number and outcomes of missing studies, and adjusts the meta-analysis to
incorporate the theoretical missing studies. The authors claim that the
method is effective and consistent with other adjustment techniques.
The user provides the effect estimate, ^theta^, to ^metatrim^ as a log risk
ratio, log odds ratio, or other direct measure of effect. Along with theta,
the user supplies a measure of theta's variability (i.e., its standard error,
^se_theta^, or its variance, ^var_theta^). Alternatively, the user may provide
the exponentiated form, ^exp(theta)^, (i.e., a risk ratio or odds ratio) and its
confidence interval, ^(ll, ul)^.
As an option, ^metatrim^ provides a funnel graph of the filled data. The funnel
graph plots ^theta^ versus ^se_theta^. Guide lines to assist in visualizing the
funnel are plotted at the variance-weighted (fixed effects) meta-analytic
effect estimate and at pseudo confidence interval limits about that effect
estimate (i.e., at ^theta +/- z * se_theta^, where ^z^ is the standard Normal
variate for the confidence level specified by option ^level()^. Each filled
(i.e., augmented) data point is indicated by the addition of a square placed
around the data symbol.
Note: ^metatrim^ requires that program ^meta^ be installed on your system.
Use ^findit meta^ to find and install ^meta^ from STB-43.
Options
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^var^ indicates that ^var_theta^ was supplied on the command line instead of
^se_theta^. Option ^ci^ should not be specified when option ^var^ is specified.
^ci^ indicates that ^exp(theta)^ and its confidence interval, ^(ll, ul)^, were
supplied on the command line instead of ^theta^ and ^se_theta^. Option ^var^
should not be specified when option ^ci^ is specified.
^reffect^ requests that the analysis be based on random-effects meta-analytic
point estimates. The default is to base the calculations on fixed-effects
meta-analytic point estimates.
^mixed^ requests that the meta-analyses during iterations be different from
those of the initial and final meta-analyses. That is, if ^reffect^ is
specified, a random-effects meta-analysis is used for the initial point
estimate and the final filled analysis but fixed-effects meta-analysis is used
for point estimates during iteration. Conversely, if the default analysis is
chosen (i.e. ^reffect^ not specified) then a fixed-effects meta-analysis is
used for the initial point estimate and the final filled analysis but random-
effects meta-analysis is used for point estimates during iteration.
^print^ requests that the weights used in the fixed and random effects
estimation are listed for each study, together with the individual study
estimates and confidence intervals. The studies are labelled by name if
the ^idvar^ option is specified, or by number otherwise.
^eform^ requests that the results in the final meta-analysis and in the ^print^
option be reported in exponentiated form. This is useful when the data
represent odds ratios or relative risks.
^estimator(^{ ^run^ | ^linear^ | ^quadratic^ }^)^ chooses the estimator to be used
to determine the number of points to trim in each iteration. The ^run^
estimator is non-robust to an isolated negative point and the ^quadratic^
estimator may not be defined when the number of points in the data set is
small. The ^linear^ estimator is stable in most situations and is the default.
^funnel^ requests the filled funnel graph showing the data, the fixed-effects
(variance-weighted) meta-analytic effect, and the pseudo confidence interval
limits about the meta-analytic effect.
^level(^#^)^ sets the confidence level % for the pseudo confidence intervals;
the default is 95%.
^idvar(^varname^)^ indicates the character variable used to label the studies.
^graph^ requests that the point estimates and confidence intervals be plotted.
The combined estimate in the graph is derived using fixed or random effects
meta-analysis, as specified by option ^reffect^.
^save(^filename [^, replace^]^)^ saves the filled data in a separate Stata data
file. The filename is assumed to have extension ^.dta^ (an extension should not
be provided by the user). If filename does not exist, it is created. If
filename exists, an error will occur unless ^replace^ is also specified. Only
three variables are saved: a study id variable and two variables containing
the filled theta and setheta values. The study id variable, named ^id^ in the
saved file, is created by ^metatrim^ but, when option ^idvar()^ is specified,
is based on that id variable. The filled theta and setheta variables are
named ^filled^ and ^sefill^ in the saved file.
^flip^ is a switch that changes the direction in which studies are assumed to be
suppressed by publication bias. By default, ^metatrim^ assumes that studies with
negative or small effect sizes are suppressed. Specifying ^flip^ causes ^metatrim^
to assume that studies with positive or large effect sizes are suppressed. Use
of this option would be appropriate, for example, where a beneficial treatment
reduces the odds or risk of death. Studies not showing the desired effect
(i.e., a decrease) may be more likely to be suppressed by publication bias.
Graph options are those allowed with ^graph, twoway^, except ^ylabel()^, ^symbol()^,
^xlog^, ^ytick^ and ^gap^ are not recognized by ^graph^. For ^funnel^, the default
graph_options include ^connect(lll..)^, ^symbol(iiioS)^, and ^pen(35522)^ for
displaying the meta-analytic effect, the pseudo confidence interval limits
(two lines), the data points, and the augmented data, respectively.
Required input variables
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^theta^ the effect estimate
^se_theta^ the corresponding standard error
or
^theta^ the effect estimate
^var_theta^ the corresponding variance
or
^exp(theta)^ the risk (or odds) ratio
^ll^ the lower limit of the risk ratio's confidence interval
^ul^ the upper limit of the risk ratio's confidence interval
[^cl^] optional (see below)
Optional input variable
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^cl^ contains the confidence level of the confidence interval defined by ^ll^
and ^ul^. If ^cl^ is not provided, the procedure assumes that each confidence
interval is at the 95% confidence level. ^cl^ allows the user to provide the
confidence level, by study, when the confidence interval is not at the default
level. ^cl^ can be specified with or without a decimal point. For example,
90 and .90 are equivalent and may be mixed (i.e., 90, .95, 80, .90 etc.).
Note
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If your data are in raw count format, program ^metan^ can be used to facilitate
conversion to effect format. ^metan^ automatically adds ^exp(theta)^ and ^se_theta^
variables to the dataset, calling them ^_ES^ and ^_seES^. You must manually
generate ^theta^ as the natural log of ^_ES^ (for example, ^gen _lnES = ln(_ES)^)
then input the effect-format variables, ^_lnES^ and ^_seES^, using ^metatrim^'s
default input method.
Examples
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. ^metatrim logrr selogrr, funnel print^
. ^metatrim logrr varlogrr if site==3, var graph^
. ^metatrim rr ll ul, ci eform reffect^
. ^metatrim logor selogor if region==4, funnel level(90)^
References
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Duval, S., Tweedie, R., 2000. A nonparametric "trim and fill" method of
accounting for publication bias in meta-analysis. JASA 95(449): 89-98.
Author
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Thomas J. Steichen, steichen@triad.rr.com
Also see
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STB: STB-57 sbe39 (STB-58 sbe-39.1; STB-61 sbe-39.2)
Manual:
On-line: help for @meta@, @metabias@, and @metan@ (if installed)