[R-meta] Coding for length of time in longitudinal studies given its use in meta-regression
Farzad Keyhan
|@keyh@n|h@ @end|ng |rom gm@||@com
Tue May 18 21:23:48 CEST 2021
Dear Michael and list members,
Thank you for your response. May I clarify the following:
1) We have a "continuous" moderator called `length` showing the "amount of
time" allowed between the last treatment and each post-test in each of our
longitudinal studies.
2) QUESTION: Since `length` is a moderator that only applies to
"post-tests" (see definition above) and NOT to the "pre-tests", would it be
accurate (i.e., from the perspective of using `length` in meta-regression)
to put "0" for all "pre-test" rows in each study when coding for `length`?
3) An example coded study (per your request, I'm also sharing a link for
easier access to this one example coded study). In this one example coded
study, descriptives are denoted by: mT,sdT,nTmC,sdC,nC. Also, 'group'
denotes the treatment group index, and 'time' is a time point indicator.
example_of_a_coded_study <- read.csv("
https://raw.githubusercontent.com/hkil/m/master/1.csv")
study mT sdT nT mC sdC nC group length time
13 xxx 67.590 19.260 17 51.900 28.320 20 1 0 0
14 xxx 67.590 19.260 17 51.900 28.320 20 1 0 0
15 xxx 53.110 21.730 18 51.900 28.320 20 2 0 0
16 xxx 53.110 21.730 18 51.900 28.320 20 2 0 0
17 xxx 59.350 18.390 20 51.900 28.320 20 3 0 0
18 xxx 59.350 18.390 20 51.900 28.320 20 3 0 0
19 xxx 82.530 14.330 17 52.750 23.260 20 1 0 1
20 xxx 77.500 16.070 18 52.750 23.260 20 2 0 1
21 xxx 81.250 13.000 20 52.750 23.260 20 3 0 1
22 xxx 82.650 15.470 17 63.900 18.890 20 1 7 2
23 xxx 76.780 20.670 18 63.900 18.890 20 2 7 2
24 xxx 80.050 12.090 20 63.900 18.890 20 3 7 2
On Tue, May 18, 2021 at 7:53 AM Michael Dewey <lists using dewey.myzen.co.uk>
wrote:
> Dear Fred
>
> I am not sure I understand what you are doing but the usual route if you
> have a variable which is only meaningful in one condition is to also
> include a two-level factor for condition.
>
> Incidentally if people need to use your data it is much better to
> include it using dput() so they can read it in directly.
>
> Michael
>
> On 17/05/2021 22:50, Farzad Keyhan wrote:
> > Dear All,
> >
> > My collaborators and I want to code for the "length of time" (`length`)
> > elapsed between the last treatment and each post-test in each of our
> > longitudinal studies (an example is below).
> >
> > My question is that since `length` is a moderator that only applies to
> > "post-tests" and NOT to the "pre-tests", is it correct (i.e., from the
> > perspective of using `length` in meta-regression) to put "0" for all
> > "pre-test" rows (up to row # 18)?
> >
> > Note that "0" is a meaningful value for `length`. For example, in the
> study
> > coded below, "post-test 1" (i.e., time == 1) has an actual `length` of
> "0".
> >
> > Thank you for your assistance,
> > Fred
> > study mT sdT nT mC sdC nC
> > group length time
> > 13 xxxxxxxxxxx 67.590 19.260 17 51.900 28.320 20 1 0
> > 0
> > 14 xxxxxxxxxxx 67.590 19.260 17 51.900 28.320 20 1 0
> > 0
> > 15 xxxxxxxxxxx 53.110 21.730 18 51.900 28.320 20 2 0
> > 0
> > 16 xxxxxxxxxxx 53.110 21.730 18 51.900 28.320 20 2 0
> > 0
> > 17 xxxxxxxxxxx 59.350 18.390 20 51.900 28.320 20 3 0
> > 0
> > 18 xxxxxxxxxxx 59.350 18.390 20 51.900 28.320 20 3 0
> > 0
> > 19 xxxxxxxxxxx 82.530 14.330 17 52.750 23.260 20 1 0
> > 1
> > 20 xxxxxxxxxxx 77.500 16.070 18 52.750 23.260 20 2 0
> > 1
> > 21 xxxxxxxxxxx 81.250 13.000 20 52.750 23.260 20 3 0
> > 1
> > 22 xxxxxxxxxxx 82.650 15.470 17 63.900 18.890 20 1 7
> > 2
> > 23 xxxxxxxxxxx 76.780 20.670 18 63.900 18.890 20 2 7
> > 2
> > 24 xxxxxxxxxxx 80.050 12.090 20 63.900 18.890 20 3 7
> > 2
> >
> > [[alternative HTML version deleted]]
> >
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> >
>
> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>
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