## Stata 15 help for mhodds

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[R] epitab -- Tables for epidemiologists (mhodds)

Syntax

mhodds var_case expvar [vars_adjust] [if] [in] [weight] [,
mhodds_options]

mhodds_options            Description
-------------------------------------------------------------------------
Options
by(varlist [, missing]) stratify on varlist
binomial(varname)       number of subjects variable
compare(v_1, v_2)       override categories of the control variable
level(#)                set confidence level; default is level(95)
-------------------------------------------------------------------------
fweights are allowed; see weight.

Statistics > Epidemiology and related > Tables for epidemiologists >
Ratio of odds of failure for two categories

Description

mhodds is used with case-control and cross-sectional data. It estimates
the ratio of the odds of failure for two categories of expvar, controlled
for specified confounding variables, vars_adjust, and tests whether this
odds ratio is equal to one.  When expvar has more than two categories but
none are specified with the compare() option, mhodds assumes that expvar
is a quantitative variable and calculates a 1-degree-of-freedom test for
trend.  It also calculates an approximate estimate of the log odds-ratio
for a one-unit increase in expvar. This is a one-step Newton-Raphson
approximation to the maximum likelihood estimate calculated as the ratio
of the score statistic, U, to its variance, V (Clayton and Hills 1993,
103).

Options

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

by(varlist [, missing]) specifies that the tables be stratified on
varlist.  Missing categories in varlist are omitted from the
stratified analysis, unless option missing is specified within by().
Within-stratum statistics are shown and then combined with
Mantel-Haenszel weights.

binomial(varname) supplies the number of subjects (cases plus controls)
for binomial frequency records.  For individual and simple frequency
records, this option is not used.

compare(v_1,v_2) indicates the categories of expvar to be compared; v_1
defines the numerator and v_2, the denominator.  When compare() is
not specified and there are only two categories, the second is
compared to the first; when there are more than two categories, an
approximate estimate of the odds ratio for a unit increase in expvar,
controlled for specified confounding variables, is given.

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

Examples

Setup
. webuse bdesop

Calculate the odds ratio for the effect of alcohol controlled for age
. mhodds case alcohol agegrp [fw=freq]

Same as above, but perform the calculation by levels of tobacco
consumption
. mhodds case alcohol agegrp [fw=freq], by(tobacco)

Calculate the odds ratio for the effect of tobacco controlled for age by
levels of alcohol consumption
. mhodds case tobacco agegrp [fw=freq], by(alcohol)

Create a new variable with levels corresponding to all combinations of
alcohol and tobacco consumption
. egen alctob = group(alcohol tobacco)

Calculate the odds ratio for the effect of the highest level of alcohol
and tobacco consumption versus the lowest
. mhodds case alctob [fw=freq], compare(16,1)

Stored results

mhodds stores the following in r():

Scalars
r(p)           two-sided p-value
r(or)          odds ratio
r(lb_or)       lower bound of CI for or
r(ub_or)       upper bound of CI for or
r(chi2_hom)    chi-squared test of homogeneity
r(df_hom)      degrees of freedom for chi-squared test of homogeneity
r(chi2)        chi-squared

Reference

Clayton, D. G., and M. Hills. 1993.  Statistical Models in Epidemiology.
Oxford: Oxford University Press.

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