<>
You should look at the column frequencies, i.e. condition on the disease
status, to get the correct picture. I also compare with official -roctab-,
and -senspec- gives the same answers:
*************
clear
vers 9.2
set obs 1000
set seed 12358
gen byte test=irecode(uniform(),0,0.33,1)
gen disease=_n>500
tab test disease, row
gen method=irecode(uniform(),0,0.5,1)
bysort method: tab test disease, row
tab test disease if method==1, /*row */ col
senspec disease test if method==1, se(sens) spe(spec) fpos(fpos) ///
ntneg(ntneg) fneg(fneg) ntpos(ntpos) nfpos(nfpos) nfneg(nfneg)
list test disease ntneg spec nfneg fneg nfpos fpos ntpos sens in 1/10
//compare to official Stata
roctab disease test if method==1, detail table
*************
If ever you are in doubt about the definitions of all these numbers, look at
*************
webuse lbw, clear
logit low age lwt i.race smoke ptl ht ui
estat clas
************
It is all defined in this last table...
HTH
Martin
-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Michael
McCulloch
Gesendet: Dienstag, 10. November 2009 21:46
An: Statalist Statalist
Betreff: st: -senspec- interpretation question
Dear Statalist folks,
I'd like to ask advice on interpreting the output of -senspec-. I've
created the following simple simulation example which allows me to
compare the -senspec- output to a simple 2x2 table. The following code
shows that the absolute numbers from -senspec- agrees with each cell
of my 2x2 table, but the frequency values are different. Am I
misinterpreting or mis-applying -senspec-?
clear
set obs 1000
set seed 12358
gen test=1 + int(2*uniform())
replace test=0 if test==2
replace test=1 in 1/300
gen disease=0 in 1/500
replace disease=1 in 501/1000
tab test disease, row
gen method=1 + int(2*uniform())
bysort method: tab test disease, row
tab test disease if method==1, row
senspec disease test if method==1, se(sens) spe(spec) fpos(fpos)
ntneg(ntneg) fneg(fneg) ntpos(ntpos) nfpos(nfpos) nfneg(nfneg)
* cellA: ntneg sp cellB: nfneg fneg cellC: nfpos fpos
cellD:
ntpos se
list test disease ntneg spec nfneg fneg nfpos fpos ntpos sens in 1/10
Thank you kindly.
Michael McCulloch
Pine Street Foundation
124 Pine Street
San Anselmo, CA 94960-2674
tel: 415-407-1357
fax: 206-338-2391
[email protected]
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