```help oeratio
-------------------------------------------------------------------------------

Title

oeratio --   ratio of observed to expected outcomes

Syntax

oeratio [{depvar predictvar}] [if] [in] [, options]

options               Description
-------------------------------------------------------------------------
Main
seonly              suppress the display; calculate only the standard
error; programmer's option
level(#)            specify confidence level; if not specified system
default is used.
-------------------------------------------------------------------------
by is allowed; see [D] by.

Description

oeratio calculates the ratio of the number of observed and expected
outcomes of note.  If depvar and predictvar (the variable specifying the
individual probability of a positive outcome for each subject) are not
specified, the command must follow a logit or logistic command.

Options

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

seonly restricts the calculation to only make calculations required to
generate the standard error and ratio of observed to expected
outcomes.

level set the confidence level. If not specified, the default confidence
level is used; see [R] level.

Remarks

The variance is calculated using the Bernoulli distribution: that is if p
is the prediction variable: variance = sum(p*(1-p)). In its current form
the standard error, confidence intervals and z-score calculated do not
take into account the error of the model.

This command was developed in order to calculate the standardized
mortality ratio (SMR) for intensive care units (ICU) when applying
logistic mortality prediction models such as MPM, APACHE, PRISM or PIM
models to unit data as part of benchmarking procedures.

Examples

---------------------------------------------------------------------------
Setup
. webuse lbw2
Logistic regression on even records
. logit low age lwt race2 race3 smoke ptl ht ui if mod(id,2)==0
Ratio of observed to expected outcomes when model applied to odd records
. oeratio if mod(id,2)==1
---------------------------------------------------------------------------
externally validated logistic regression model covariates applied to lbw
data
. generate p = invlogit(-2 + (0.05* age))
. oeratio low p
---------------------------------------------------------------------------

Saved Results

logit saves the following in r():

Scalars
r(N)           number of observations
r(predicted)   number of outcomes predicted
e(obs)         number of outcomes observed
e(ratio)       ratio of observed to predicted outcomes
e(se)          standard error
e(z)           z score of the difference between observed and predicted
outcome

Also see

Calculating standardised mortality rate (as opposed to ratio) [ST]
stptime;
```