04.06.2013 Views

Introduction to Stata 8 - (GRIPS

Introduction to Stata 8 - (GRIPS

Introduction to Stata 8 - (GRIPS

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Including age in the analysis<br />

stset data with ageout as the time-of-exit variable, agein as the time-of-entry<br />

variable:<br />

. // c:\dokumenter\proj1\gen.st.cancer2.do<br />

. use c:\dokumenter\proj1\cancer1.dta , clear<br />

. stset ageout , enter(time agein) failure(died==1) id(lbnr)<br />

. summarize<br />

Variable | Obs Mean Std. Dev. Min Max<br />

-------------+-----------------------------------------------------<br />

lbnr | 48 24.5 14 1 48<br />

... |<br />

_st | 48 1 0 1 1<br />

_d | 48 .6458333 .4833211 0 1<br />

_t | 48 57.61966 5.444583 49.87939 68.70284<br />

_t0 | 48 56.328 5.659862 47.97637 67.73915<br />

. save c:\dokumenter\proj1\st.cancer2.dta<br />

The sts and stcox analyses as shown above now must be interpreted as age-adjusted<br />

(delayed entry analysis). Summary of time at risk and age-specific incidence rates:<br />

stptime , at(45(5)70) by(drug) // 5 year age intervals<br />

stsplit [ST] stsplit<br />

To look at the influence of age at incidence or survival, stsplit the data, expanding each<br />

observation <strong>to</strong> an observation for each age interval:<br />

. // c:\dokumenter\proj1\gen.stsplit.cancer2.do<br />

. use c:\dokumenter\proj1\st.cancer2.dta , clear<br />

. stsplit agegr , at(45(5)70)<br />

. summarize<br />

Variable | Obs Mean Std. Dev. Min Max<br />

-------------+-----------------------------------------------------<br />

lbnr | 61 26.37705 14.03586 1 48<br />

drug | 61 1.967213 .8557105 1 3<br />

drug01 | 61 .6229508 .4886694 0 1<br />

agein | 61 55.58628 5.651005 47.09552 67.87458<br />

ageout | 61 56.87054 5.563221 49.01218 68.8737<br />

risktime | 61 1.412568 .8856398 .0833333 3.25<br />

died | 48 .6458333 .4833211 0 1<br />

_st | 61 1 0 1 1<br />

_d | 61 .5081967 .5040817 0 1<br />

_t | 61 56.87054 5.563221 49.01218 68.8737<br />

_t0 | 61 55.85415 5.610502 47.09552 67.87458<br />

agegr | 61 54.01639 5.832357 45 65<br />

. save c:\dokumenter\proj1\stsplit.cancer2.dta<br />

The data now has 61 observations with events and risktime distributed <strong>to</strong> the proper age<br />

intervals. Describe risktime etc. by:<br />

bysort drug: stsum , by(agegr)<br />

36

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!