Dear Stata Users,
thanks to Matthias Mohner a bug has been found and fixed in -stcascoh-,
a command used for case-cohort analysis.
The new version is available for download on the SSC Archive.
Here is some more detail for people interested in this topic
The problem occurs when the data need not to be sampled. i.e when they
already consist of subcohort sample and of non-subcohort cases.
In this cases -stcascoh- can still be applied to appropriately generate
the observations for the next Cox model eventually with Self-Prentice
variance estimator (-stselpre- command).
The steps are as follows:
1) Divide the data set in two files: the first one for subcohort
observations, the second for additional cases.
2) Appropriately -stset- the new files.
3) Process the subcohort file with -stcascoh- setting alpha just below 1
(i.e. .999) and save this file.
Do some assert to verify that _subco _wSelpre _wBarlow are coded as you
expect.
4) Process the additional cases file with -stcascoh- setting alpha = 0
and save this second file.
Also for this file some -assert- is appropriate to verify that _subco
_wSelpre _wBarlow are coded as you expect.
5) Append the two files you generated.
6) Adapt the Barlow weights.
Suppose you sampled 1000 out of 16000 subjects.
You should type
replace _wBarlow=ln(16000/1000) if _wBarlow>0
Well, after using these codes, the old version of -stcascoh- does not
allow to use -stselpre-. This has been fixed.
Best wishes
Enzo
--
Enzo Coviello
Unità di Epidemiologia e Statistica ASL BARI
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Italy
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