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

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 at 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

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--
Michael
http://www.dewey.myzen.co.uk/home.html