[R-meta] Adjust the scale for x-axis using forest() function in the metafor package

[Viechtbauer, Wolfgang (SP)]

Dear Thao,

To be precise, you transformed the values shown on the x-axis back (through exponentiation) via the 'atransf' argument. Since exp() is a non-linear transformation, the spacing of the ticks will not be equidistant if the spacing on the log scale was equidistant to begin with (and vice-versa). Alternatively, you could use the 'transf' argument, which actually transforms all values back (not just the x-axis values that are shown). Then the spacing of the ticks will be equidistant (assuming that's how you specify the position of the ticks), but the CIs will no longer be symmetric (and appear to be of unequal widths even if the CIs are actually of equal width on the log scale). Compare:

yi <- log(c(.8, 1, 1.2, 1.4))
vi <- rep(.01, 4)
forest(yi, vi)
forest(yi, vi, atransf=exp, at=log(c(.5, 1, 1.5, 2)))
forest(yi, vi, transf=exp, at=c(.5, 1, 1.5, 2))

Best,
Wolfgang

>-----Original Message-----
>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org]
>On Behalf Of Thao Tran
>Sent: Tuesday, 16 June, 2020 10:06
>To: Michael Dewey
>Cc: r-sig-meta-analysis using r-project.org
>Subject: Re: [R-meta] Adjust the scale for x-axis using forest() function in
>the metafor package
>
>Hey Michael,
>It is indeed a plot on the log-scale.
>However, I did transform the values back to the original scale using
>atransf = exp.
>It is quite intuitive to see the 95% CI on the linear scale so the
>variabilities of different studies can be seen clearly.
>If you take a look at the plot above (in the previous email): the first
>study had a very wide 95% CI (on the plot) although the values vary only
>between 10 and 99.
>The Roghmann study (fifth from the top) had a wide CI (from 400 to 1300)
>but shows very short CI on the plot.
>
>Regards,
>Thao
>
>On Mon, Jun 15, 2020 at 7:15 PM Michael Dewey <lists using dewey.myzen.co.uk>
>wrote:
>
>> Dear Thao
>>
>> It is not wuite clear to me why you expect to see a linear scale on a
>> plot using log values. I would suggest putting the ticks at places more
>> evenly spaced on the log scale.
>>
>> Michael
>>
>> On 15/06/2020 16:32, Thao Tran wrote:
>> > Dear,
>> > I want to plot an rma object using the forest() function in the metafor
>> > package.
>> > Here is a reproducible code to run it (please see the attachment).
>> >
>> > axis.png
>> >
>> > The problem is the x-axis does not scale as I expected even I tried
>> > using at = ...
>> > I wanted to have the x-axis scale from 1, to 1000 but with equal
>> > interval, for example, between (0, 1e2), (1e2, 2e2), (2e2, 3e2)...
>> >
>> 1-----100-----200-----300-----400-----500-----600-----700-----800-----900-
>---1000
>> > (something similar).
>> >
>> > Do you have any suggestions?
>> > Regards
>> > Thao
>> > --
>> > /Trần Mai Phương Thảo/
>> > Master Student - Master of Statistics
>> > Hasselt University - Belgium.
>> > Email: Thaobrawn using gmail.com <mailto:Thaobrawn using gmail.com> /
>> > maiphuongthao.tran using student.uhasselt.be
>> > <mailto:maiphuongthao.tran using student.uhasselt.be>
>> > Phone number: + 84 979 397 410+ 84 979 397 410/ 0032 488 0358430032 488
>> > 035843