On Wednesday Scott asked about missing values with multiple record
survival data:
I am missing data for certain time-
variant covariates when t is very small. ...
...for all values of t=0 to t=9, I am missing data for sr.
.... assume I wanted to fill in those missing
values with the same value as t=10. How would I do this?
The Stata command -stfill- is very useful for replacing
values in covariates of multiple record survival data.
With the option -baseline- it replaces all observations
with the earliest value observed. With the option
-forward- it replaces all missing values with the previous
value observed. This is similar to what Scott needs, but
not exactly: Scott needs to replace missing values with the
next value observed.
We can acheive this with careful sorting and replacing.
I will use the command -gsort- to sort the data
in reverse chronological order and then use -replace-:
clear
input id time fail sr
1 1 0 .
1 2 0 .
1 3 0 .
1 4 0 .
1 5 0 .
1 6 0 .
1 7 0 .
1 8 0 .
1 9 0 .
1 10 0 .9738716
1 11 0 1.081043
1 12 0 1.21261
1 13 1 1.125889
2 1 0 .
2 2 0 .
2 3 0 .
2 4 0 .
2 5 0 .
2 6 0 .
2 7 0 .
2 8 0 .
2 9 0 .
2 10 0 .9738716
2 11 0 1.081043
2 12 0 1.21261
2 13 0 1.125889
2 14 0 1.080463
2 15 1 .9527455
end
list, sepby(id)
stset time, id(id) fail(fail)
list, sepby(id)
gsort id -_t
replace sr=sr[_n-1] if sr==.
sort id _t
list, sepby(id)
-- May
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