Stata 4, Survival

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Stata 4, Survival

• Hein Stigum
• Presentation, data and programs at
• http//folk.uio.no/heins/

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Agenda

• Kaplan-Meier plots
• Cox regression
• Example
• Age at first intercourse

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Survival data
Outcome

• Unajusted analysis
• Kaplan-Meier
• Regression method
• Cox-regression

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Survival data setup

• Status and time
• generate status!missing(DebutAge)
• generate timeDebutAge
• replace timeAge if status0
• generate time2timeuniform() avoid ties
• Set and describe
• stset time, failure(status1) Set data
• stdes Describe

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Setting the timescale
Time time since diagnosis in years stset
dateexit, failure(dead1) origin(datediag)
scale(365.25)
Time age in years stset dateexit,
failure(dead1) origin(datebth) enter(datediag)
scale(365.25)
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Mathematical functions

• Standard distribution functions
• Time to event T
• Density f(t)
• Cumulative density F(t)
• Survival functions

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Some relationships
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Kaplan-Meier

• Survival function
• Syntax
• sts graph, by(sex) KM survival plot
• sts test sex log-rank test
• stci, p(50) by(sex) time to 50 failure
• sts list, at(5 10 30) survival at time 5,

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Kaplan-Meier, all
sts graph, fail gwood tmin(8) tmax(30) noorigin
Age at 50 failure stci, p(50) 18.4 (18.1,18.8)
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Kaplan-Meier, by sex
sts graph, fail by(gender) tmin(8) tmax(30)
noorigin
Age at 50 failure stci, p(50) by
(gender) Males 18.6 (18.3,19.0) Females
18.1(17.8,18.9)
Log-rank test sts test gender p-value0.3
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Hazards
sts graph, hazard by(gender) width(2)
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Cox regression

• Model
• Syntax
• stcox x1 x2
• Proportional hazard test
• stcox x1 x2, schoenfeld(sc) scaledsch(ssc)
• estat phtest, detail
• estat phtest, plot(x1)

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Full model
stcox gender cohab partfrq
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Proportion hazard test
Save residuals stcox gender cohab partfrq,
schoenfeld(sc) scaledsch(ssc) Test estat
phtest, detail
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Smoothed Schoenfeld residuals
estat phtest, plot(cohab)
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Baseline hazard
stcox gender cohab partfrq, basesurv(bsurv)
basehc(bhaz) stcurve, hazard at(gender1 cohab1
partfrq0) range(8 30) width(1)
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Predicted survival
stcurve, survival at1(gender1 cohab1
partfrq0) at2(gender2 cohab1 partfrq0)
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If proptional hazard fails

• Stratified Cox regression
• Separate analysis on time intervals
• Time dependent covariats
• Additive model

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Some Cox options

• stcox drug age, strata(sex) Stratified
• stcox drug age, shared(family) Frailty
• stcox drug age, tvc(varlist) Timevar cov