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help for ^mhrate^                                              (STB-27: ssa7)
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Calculation of rate ratios
--------------------------

    ^mhrate^ fail xvar [varlist] [^if^ exp] [^in^ range] ^e^xposure^(^fup^)^
		[^,^ ^by(^varlist^)^ ^c^ompare^(^val1^,^val2^)^ ^l^evel^(^#^)^]


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

^mhrate^ estimates the ratio of the rates of failure for categories ^val1^ and
^val2^ of the explanatory variable, ^xvar^. The failure variable indicates
failure (1) or censoring (0) after a time which is in the follow-up variable
supplied in ^exposure^.  Alternatively, ^mhrate^ may be used with records
where the failure variable contains the total number of failures for each
combination of explanatory variables, and the follow-up variable contains the
corresponding person-years observation.

The optional ^varlist^ contains 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 odds ratio
with further categorical variables may be explored.


Options
-------

^exposure(^varname^)^ specifies the variable containing the person-years of
    observation time (expected numbers with SMRs).

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

^compare(^val1^,^val2^)^ specifies the categories of xvar to be compared.  ^val1^
    defines the numerator and ^val2^ the denominator. When ^compare^ is absent and
    there are only two categories, the second is compared to the first; when
    there are more than two categories the rate ratio for a unit increase in
    ^xvar^, controlled for specified confounding variables, is given.

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


Examples
--------

 . ^mhrate d smoke age, c(2,1) e(y) by(sex)^  -- Individual records
					         Controlled for age, by sex

 . ^mhrate D smoke age, c(2,1) e(Y) by(sex)^  -- Poisson frequency records
					         Controlled for age, by sex

 . ^mhrate d smoke age sex, c(2,1) e(y)^      -- Individual records
					         Controlled for age and sex


Authors
-------

        David Clayton, MRC Biostatistical Research Unit, Cambridge
        david.clayton@@mrc-bsu.cam.ac.uk
        Michael Hills, London School of Hygiene and Tropical Medicine, London
        mhills@@lshtm.ac.uk


Also see
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    STB:  STB-27 ssa7
On-line:  help for @lexis@ and @tabrate@