[R-meta] Coding for length of time in longitudinal studies given its use in meta-regression

[Farzad Keyhan]

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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