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help for ^smrby^                                        (STB-29: sg29.1)
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Tabulation of observed/expected ratios and exact confidence intervals
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        ^smrby^ obsvar expvar [^if^ exp] [^in^ range] [^,^ ^by(^byvar^)^
            ^h^etero ^l^evel^(^#^)^ ^o^rdinal ^tot^al ^tr^end ]


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

For each different value of the optional ^byvar^, ^smrby^ computes the ratio of
the sum of the observed counts in ^obsvar^ over the sum of the expected counts
in ^expvar^, together with a confidence interval based on assuming that ^obsvar^
is distributed Poisson with expected value ^expvar^.  A one-sided confidence
interval is provided if the observed count is zero.  Significant ratios are
marked: * p<.05, ** p<.01, *** p<.001. All p-value's and confidence intervals
are unadjusted for the implicit multiple comparisons.  p-values are twice the
one-sided Poisson probabilities of observing a more extreme count. 


Options
-------

^by(^byvar^)^ specifies groups for which the observed/expected ratios are to be
    calculated separately.  ^byvar^ is a numeric or string variable that is used
    to label the rows of the table.  If ^byvar^ is not an integer, it is
    advisable to read and store it as a ^double^ rather than as a ^float^ to
    avoid unattractive display.  If the ^by()^ option is not specified, ^smrby^
    will treat each observation as a separate group.  (See the ^total^ option.)

^hetero^ produces the chi-squared test for unequal SMRs (heterogeneity).

^level^ specifies the significance level in percent for the confidence interval.

^ordinal^ this option is only effective in conjunction with the ^trend^ option. 

^total^ specifies that the total observed count together with its expectation,
    the ratio O/E and the confidence interval should be calculated and
    displayed in addition to the usual output.

^trend^ produces the score test for a linear trend in SMRs against the ^byvar^.
    If the ^ordinal^ option is also specified, then the test is carried out
    using the values 1,2,3...


Examples
--------

 . ^smrby obs exp if icd<155 & icd>145, by(icd_f)^


Author
------

        Peter Sasieni, Ph.D.
        Imperial Cancer Research Fund
        FAX  011-44-171-269-3429


Also see
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    STB:  STB-29 sg29.1, STB-23 sg29
On-line:  help for @smr@ (if installed)