Hi,
Thanks for the reply. Much appreciated!
I couldn't quite get my head around the bysort clause where you stated
"keep if _n==_N". Is it that the clause essentially states, by patient
section, sort the time entries, and keep the entries where the current
observation is equal to the total number of observations in the dataset? I
don't understand logic behind this clause. Sorry this is such an elementary
question. ...
Any help is appreciated!
Lucy
Quoting Joseph Coveney <c>:
Lucy Shum wrote:
Hi all, could anybody advise on how to specify in STATA, analysis of
specific groups within a category? That is, if I have a category called
events_mastitis - there are 7 different groups meaning there are animals
that experienced between 1 - 7 episodes of mastitis within a lactation.
Say
if I only want STATA to analyze, tabulate, create graphs of.., say Group
1
and 5 only. How do I go about doing that?
Also, using the example above, how do I go about writing a command so
that
STATA compares the survival estimates of these 7 groups? Logrank? Is
there a
modified procedure that deals with comparison of greater than 2 groups?
--------------------------------------------------------------------------------
You can use -inlist()- to select groups:
tabulate pathogen if inlist(events_mastitis, 1, 5)
You can use Stata's survival commands for comparing more than two
groups.
The example below creates four groups (age categories) and peforms a
log-rank test and Cox regression.
Joseph Coveney
use http://www.stata-press.com/data/r9/catheter, clear
bysort patient (time): keep if _n == _N
egen byte age_category = cut(age), group(4)
stset time, failure(infect)
sts test age_category
xi: stcox i.age_category
exit
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