Stata 15 help for stptime

[ST] stptime -- Calculate person-time, incidence rates, and SMR


stptime [if] [, options]

options Description ------------------------------------------------------------------------- Main at(numlist) compute person-time at specified intervals; default is to compute overall person-time and incidence rates trim exclude observations <= minimum or > maximum of at() by(varname) compute incidence rates or SMRs by varname

Options per(#) units to be used in reported rates dd(#) number of decimal digits to be displayed smr(groupvar ratevar) use groupvar and ratevar in using() dataset to calculate SMRs using(filename) specify filename to merge that contains smr() variables level(#) set confidence level; default is level(95) noshow do not show st setting information

Advanced jackknife jackknife confidence intervals title(string) label output table with string output(filename [,replace]) save summary dataset as filename; use replace to overwrite existing filename ------------------------------------------------------------------------- You must stset your data before using stptime; see [ST] stset. by is allowed; see [D] by. fweights, iweights, and pweights may be specified using stset; see [ST] stset.


Statistics > Survival analysis > Summary statistics, tests, and tables > Person-time, incidence rates, and SMR


stptime calculates person-time and incidence rates. stptime computes standardized mortality/morbidity ratios (SMRs) after merging the data with a suitable file of standard rates specified with the using() option.


+------+ ----+ Main +-------------------------------------------------------------

at(numlist) specifies intervals at which person-time is to be computed. The intervals are specified in analysis time t units. If at() is not specified, overall person-time and incidence rates are computed.

If, for example, you specify at(5(5)20) and the trim option is not specified, person-time is reported for the intervals t = (0 - 5], t = (5 - 10], t = (10 -15], and t = (15 - 20].

trim specifies that observations less than or equal to the minimum or greater than the maximum value listed in at() be excluded from the computations.

by(varname) specifies a categorical variable by which incidence rates or SMRs are to be computed.

+---------+ ----+ Options +----------------------------------------------------------

per(#) specifies the units to be used in reported rates. For example, if the analysis time is in years, specifying per(1000) results in rates per 1,000 person-years.

dd(#) specifies the maximum number of decimal digits to be reported for rates, ratios, and confidence intervals. This option affects only how values are displayed, not how they are calculated.

smr(groupvar ratevar) specifies two variables in the using() dataset. The groupvar identifies the age-group or calendar-period variable used to match the data in memory and the using() dataset. The ratevar variable contains the appropriate reference rates. stptime then calculates SMRs rather than incidence rates.

using(filename) specifies the filename that contains a file of standard rates that is to be merged with the data so that SMRs can be calculated.

level(#) specifies the confidence level, as a percentage, for confidence intervals. The default is level(95) or as set by set level.

noshow prevents stptime from showing the key st variables. This option is seldom used because most people type stset, show or stset, noshow to set whether they want to see these variables mentioned at the top of the output of every st command; see [ST] stset.

+----------+ ----+ Advanced +---------------------------------------------------------

jackknife specifies that jackknife confidence intervals be produced. This is the default if pweights or iweights were specified when the dataset was stset.

title(string) replaces the default "person-time" label on the output table with string.

output(filename [, replace]) saves a summary dataset in filename. The file contains counts of failures and person-time, incidence rates (or SMRs), confidence limits, and categorical variables identifying the time intervals. This dataset could be used for further calculations or simply as input to the table command.

replace specifies that filename be overwritten if it exists. This option is not shown in the dialog box.


--------------------------------------------------------------------------- Setup . webuse stptime

List part of the data . list in 1/5

Declare data to be survival-time data . stset year, fail(fail) id(id) noshow

Calculate person-time and incidence rate . stptime

Calculate person-time and incidence rate per 1,000 person-years . stptime, per(1000)

Same as above, but tabulate in ten-year intervals and display rates to four decimal places . stptime, per(1000) at(0(10)40) dd(4)

--------------------------------------------------------------------------- Setup . webuse diet

Declare data to be survival-time data . stset dox, origin(time dob) enter(time doe) id(id) scale(365.25) fail(fail==1 3 13) noshow

Calculate person-time and incidence rates per 1,000 person-years, tabulating in ten-year intervals, and excluding observations <=40 or >70 . stptime, per(1000) at(40(10)70) trim

Calculate standardized mortality ratios using ageband and rate in smrchd.dta . stptime, smr(ageband rate) using( per(1000) at(40(10)70) trim

Calculate person-years and incidence rates per 1,000 person-years by categories of hienergy . stptime, per(1000) by(hienergy)

Same as above, but tabulating in ten-year intervals, and excluding observations <=40 or >70 . stptime, per(1000) by(hienergy) at(40(10)70) trim

Same as above, but compute the SMR using ageband and rate in smrchd.dta . stptime, smr(ageband rate) using( per(1000) by(hienergy) at(40(10)70) trim ---------------------------------------------------------------------------

Video example

How to calculate incidence rates and incidence-rate ratios

Stored results

stptime stores the following in r():

Scalars r(ptime) person-time r(failures) observed failures r(rate) failure rate r(expected) expected number of failures r(smr) standardized mortality ratio r(lb) lower bound for SMR r(ub) upper bound for SMR

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