.-
help for ^stmc^                                       (STB-40.1: ssa10.1)
.-

Calculation of rate ratios using ^st^ data
----------------------------------------

^stmc^ variable [varlist] [^if^ exp] [^in^ range], [^by(^varlist^)^ 
       ^c^ompare^(^rule1^,^rule2^)^ ^fc^odes^(^rule^)^ ^nom^iss 
       ^or^igin^(^varname^)^ ^l^evel^(^#^)^]


Description
-----------

^stmc^ carries out Mantel-Cox calculations to estimate rate
ratios. These are Mantel-Haenszel calculations in which
stratification is, very finely, by a time scale.  In its simplest use,
^stmc^ estimates the ratio of the rates of failure controlled for time
(using a proportional hazards model) for two categories of the
explanatory variable (the first argument). Categories to be compared
may be defined, as ^recode^ rules, in the ^compare^ option.
Alternatively the command may be used to carry out trend tests for a
metric explanatory variable. In this latter case a one-step Newton
approximation to the log-linear Poisson regression coefficient is also
computed. The time scale to be stratified is defined in terms of its
origin.

The remaining variables before the comma are further categorical variables 
which are to be controlled for using stratification. Strata are defined
by cross-classification by all of these variables and the rate ratio 
estimate is combined over strata using the Mantel-Haenszel method. 
Using the ^by^ option, the variation of the rate ratio with further 
categorical variables may be explored.

Upon completion, the macro ^S_1^ contains the overall Mantel-Haenszel 
estimate of the rate ratio, thus facilitating bootstrap and jackknife 
evaluation of confidence intervals.


Options
-------

^by(^varlist^)^ specifies categorical variables by which the rate ratio 
is to be tabulated. A separate rate ratio produced for each category
or combination of categories, and a test for unequal separate rate ratios 
is given. The same applies when the rate ratio for a unit increase in
xvar is given in place of the rate ratio.

^compare(^rule1^,^rule2^)^ defines, as ^recode^ rules,  the categories of 
the exposure variable to be compared; rule1 defines the numerator and rule2 
the denominator. When ^compare^ is absent and there are only two categories, 
the larger is compared to the smaller; when there are more than two categories
an analysis for (log-linear) trend is carried out.

^fcodes()^ specifies a recode rule for the failure indicator in the ^st^
data. All codes matching the rule are treated as failures and all others 
as censoring. 

^nomiss^ specifies that only cases that have no missing values for any 
stratifying variables should be included. Otherwise missing values will 
define new strata in the analysis.

^origin(^varname^)^ defines the origin for the time scale used in the analysis.

^level(^#^)^ gives the level for the confidence intervals (default 95).

Examples
--------

^stmc smoke, c(2,1) or(dob) by(sex)^ - RR for smoking controlled for age, by sex

^stmc smoke sex, or(dob) c(2,1)^     - RR for smoking controlled for age and sex

^stmc ncigs sex, or(dob)^            - Trend analysis for cigarettes/day  

^stmc ncigs sex, or(dob) c(21/max,1/20)^ - Heavy smoking vs light smoking


Authors
-------

      David Clayton
      MRC Biostatistical Research Unit
      Cambridge
      email: david.clayton@@mrc-bsu.cam.ac.uk

      Michael Hills
      London School of Hygiene and Tropical Medicine (retired)
      email: mhills@@regress.demon.co.uk


Also see
--------

    STB:  STB-41 ssa10.1, STB-40 ssa10
On-line:  help for @stmh@, @dymh@, @staalen@, @stlexis@