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

[Farzad Keyhan]

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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