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

[Michael Dewey]

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]]
> 
> _______________________________________________
> R-sig-meta-analysis mailing list
> R-sig-meta-analysis using r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-meta-analysis
> 

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