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168 lines
6.5 KiB
Plaintext
168 lines
6.5 KiB
Plaintext
{smcl}
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{* 19aug2003}{...}
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{hline}
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help for {hi:metafunnel} {right:dialog: {dialog metafunnel}{space 20}}
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{hline}
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{title:Funnel plots for meta-analysis}
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{p 8 15 2}
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{cmd:metafunnel}
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{it:{ theta { se | var } | exp(theta) ll ul [cl] }}
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[{cmd:if} {it:exp}]
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[{cmd:in} {it:range}]
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[{cmd:,}
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{cmdab:ef:orm}
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{cmdab:nol:ine}
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{cmdab:rev:erse}
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{cmdab:forc:enull}
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{cmdab:graph_options}
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]
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{title:Description}
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{p 4 4 2}
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{cmd:metafunnel} plots funnel plots. These graphical displays are used to
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examine whether the results of a meta-analysis may have been affected by
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publication or other types of bias.
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{title:Options}
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{p 4 8 2}
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{cmd:by(}{it:byvarname}{cmd:)} displays subgroups according to the value
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of {it: byvarname}. The legend
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displays the value labels for the levels of {it: byvarname} if these are
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present; otherwise it displays the value of each level of{it: byvarname}.
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{p 4 8 2}
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{cmd:eform} exponentiates the treatment effect theta and displays the
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horizontal axis (treatment effect) on a log scale. This is useful for
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displaying ratio measures such as odds ratios and risk ratios.
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{p 4 8 2}
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{cmd:reverse} inverts the funnel plot so that larger studies are displayed
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at the bottom of the plot with smaller studies at the top.
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This may also be achieved by specifying {cmd:noreverse} as part of the
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{cmd: yscale(}{it:axis_description}{cmd:)} graphics option.
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{p 4 8 2}
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{cmd:noline} specifies that pseudo 95% confidence interval lines
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should not be included in the plot. The default is to include them.
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{p 4 8 2}
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{cmd:forcenull} forces the vertical line at the centre of the funnel
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to be plotted at the null treatment effect of zero (1 when the treatment
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effect is exponentiated). The default is for the line to be plotted at
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the value of the fixed effect summary estimate.
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{title:Remarks}
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{p 4 4 2}
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Funnel plots are simple graphical displays of a measure of study size
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on the vertical axis against intervention or treatment effect on the
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horizontal axis. The name "funnel plot" is based on the fact that the
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precision in the estimation of the underlying intervention or treatment
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effect will increase as the size of component studies increases. Results
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from small studies will therefore scatter more widely, with the spread
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narrowing among larger studies. In the absence of bias the plot will
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resemble a symmetrical inverted funnel.
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{p 4 4 2}
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If there is bias, for example because smaller studies showing no
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statistically significant effects remain unpublished, then such
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publication bias will lead to an asymmetrical appearance of the funnel
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plot. It should be noted that although funnel plots have traditionally
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been used to examine evidence for publication bias, funnel plot asymmetry
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may reflect other types of bias, or even result from the true intervention
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or treatment effect differing between small and large studies. They should
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thus be seen as displaying the evidence for "small study effects" in general
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rather than publication bias in particular. These issues are discussed by
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Egger {it: et al.} (1997) and Sterne {it:et al.} (2001a).
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{p 4 4 2}
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{cmd:metafunnel} uses the same syntax as other meta-analysis commands
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such as {help meta}, {help metabias}, {help metainf} and {help metatrim}.
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The user provides an estimate of the treatment or intervention effect,
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{it: theta}, together with its associated standard error {it: se_theta}
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(the default) or variance {it: var_theta}, (in which case the {cmd: var}
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option should be specified). Alternatively, the user provides {it:exp(theta)}
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(i.e., a risk ratio or odds ratio) and its confidence interval,
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{it: (ll, ul)}).
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{p 4 4 2}
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The funnel plots are displayed in line with meta-analytic convention and
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the recommendations of Sterne et al. (2001b). The effect of the
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treatment or intervention in each study (horizontal axis) is plotted
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against the study size, as measured by the standard error of the treatment
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or intervention effect.
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(vertical axis). The vertical axis is reversed so that larger studies are
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displayed towards the top of the graph (this behaviour may be changed using
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the {cmd: reverse} option). Users who wish to plot the treatment effect on the vertical axis should use the {cmd:graph(begg)} option of
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the {help metabias} command. The {help funnel} command, which is part
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of the {help metan} package, also provides an alternative way to draw
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funnel plots.
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{p 4 4 2}
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The plots include pseudo-95% confidence interval lines, which are
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drawn around the summary fixed-effect estimate of the intervention or
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treatment effect. The lines may be omitted using the {cmd:nolines} option.
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The user may also specify that the pseudo confidence limits are centred
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around a zero intervention effect using the {cmd:forcenull} option.
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{p 4 4 2}
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When the {cmd:eform} option is used, the label of the horizontal axis
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(treatment effect, {it:theta}) is
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changed accordingly, unless there is a variable label for {cmd: theta} or
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the {cmd: xtitle(}{it:axis_title}{cmd:)} graphics option is used.
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{p 4 4 2}
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By default, the subtitle "Funnel plot with pseudo 95% confidence limits"
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is displayed. This may be changed using the graphics option
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{cmd:subtitle(}{it:tinfo}{cmd:)}.
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{title:Examples}
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{p 4 8 2}{cmd:. metafunnel meandiff semeandiff}
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{p 4 8 2}{cmd:. metafunnel logor selogor, eform xtitle("Odds ratio (log scale)")}
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{p 4 8 2}{cmd:. metafunnel sttd stderr, by(dose) subtitle(Funnel plot with subgroups) forcenull}
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{p 4 8 2}{cmd:. metafunnel logor varlogor, var reverse nolines xtitle(log odds ratio)}
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{title:Acknowledgements}
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{p 4 4 2}
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{cmd:metafunnel} was written by Jonathan Sterne, University of Bristol.
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Portions of the code were originally written by Tom Steichen, who also
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gave helpful comments on an early version of the command and provided
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the dialog.
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{title:References}
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{p 4 8 2}Egger, M., Davey Smith, G., Schneider, M., & Minder, C. (1997).
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Bias in meta-analysis detected by a simple, graphical test.
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{it:British Medical Journal} 315: 629-634
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{p 4 8 2}Sterne, J.A.C., Egger, M. and Davey Smith, G. (2001a).
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Investigating and dealing with publication and other biases
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in meta-analysis. {it: British Medical Journal} 323: 101-105
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{p 4 8 2}Sterne, J.A.C. & Egger, M. (2001b). Funnel plots for detecting
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bias in meta-analysis: guidelines on choice of axis.
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{it: Journal of Clinical Epidemiology} 54: 1046-1055
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{title:Also see}
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{p 4 13 2}
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Online: help for {help meta}, {help metabias},
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{help metainf}, {help metatrim}, {help metan}, {help funnel} (if installed)
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{p_end}
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