Stata 15 help for ir

[R] epitab -- Tables for epidemiologists (ir and iri)

Syntax

ir var_case var_exposed var_time [if] [in] [weight] [, ir_options]

iri #a #b #N1 #N2 [, level(#)]

ir_options Description ------------------------------------------------------------------------- Options by(varname [, missing]) stratify on varname estandard combine external weights with within-stratum statistics istandard combine internal weights with within-stratum statistics standard(varname) combine user-specified weights with within-stratum statistics pool display pooled estimate nocrude do not display crude estimate nohom do not display homogeneity test ird calculate standard incidence-rate difference level(#) set confidence level; default is level(95) ------------------------------------------------------------------------- fweights are allowed; see weight.

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ir Statistics > Epidemiology and related > Tables for epidemiologists > Incidence-rate ratio

iri

Statistics > Epidemiology and related > Tables for epidemiologists > Incidence-rate ratio calculator

Description

ir is used with incidence-rate (incidence-density or person-time) data. It calculates point estimates and confidence intervals for the incidence-rate ratio and difference, along with attributable or prevented fractions for the exposed and total population. iri is the immediate form of ir; see immed. Also see [R] poisson and [ST] stcox for related commands.

Options

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

by(varname [, missing]) specifies that the tables be stratified on varname. Missing categories in varname 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. If estandard, istandard, or standard() is also specified (see below), the weights specified are used in place of Mantel-Haenszel weights.

estandard, istandard, and standard(varname) request that within-stratum statistics be combined with external, internal, or user-specified weights to produce a standardized estimate. These options are mutually exclusive and can be used only when by() is also specified. (When by() is specified without one of these options, Mantel-Haenszel weights are used.)

estandard external weights are the person-time for the unexposed controls.

istandard internal weights are the person-time for the exposed controls. istandard can be used to produce, among other things, standardized mortality ratios (SMRs).

standard(varname) allows user-specified weights. varname must contain a constant within stratum and be nonnegative. The scale of varname is irrelevant.

pool specifies that, in a stratified analysis, the directly pooled estimate also be displayed. The pooled estimate is a weighted average of the stratum-specific estimates using inverse-variance weights, which are the inverse of the variance of the stratum-specific estimate. pool is relevant only if by() is also specified.

nocrude specifies that in a stratified analysis the crude estimate -- an estimate obtained without regard to strata -- not be displayed. nocrude is relevant only if by() is also specified.

nohom specifies that a chi-squared test of homogeneity not be included in the output of a stratified analysis. This tests whether the exposure effect is the same across strata and can be performed for any pooled estimate -- directly pooled or Mantel-Haenszel. nohom is relevant only if by() is also specified.

ird may be used only with estandard, istandard, or standard(). It requests that ir calculate the standardized incidence-rate difference rather than the default incidence-rate ratio.

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 irxmpl

List the data . list

Calculate incidence-rate ratios, differences, etc. . ir cases exposed time

Immediate form of above command . iri 15 41 19017 28010

--------------------------------------------------------------------------- Setup . webuse rm

List the data . list

Perform stratified analysis of the incidence-rate ratio . ir deaths male pyears, by(age)

Same as above, but report 90% confidence intervals . ir deaths male pyears, by(age) level(90)

--------------------------------------------------------------------------- Setup . webuse dollhill2

List the data . list

Perform stratified analysis of the incidence-rate ratio, reporting 90% confidence intervals . ir deaths smokes pyears, by(age) level(90)

Perform stratified analysis of the standardized incidence-rate ratio, reporting 90% confidence intervals . ir deaths smokes pyears, by(age) level(90) istandard

Same as above, but also display the directly pooled estimate . ir deaths smokes pyears, by(age) level(90) istandard pool

Same as above, but compute the standardized incidence-rate difference, rather than the incidence-rate ratio . ir deaths smokes pyears, by(age) level(90) istandard pool ird

Perform stratified analysis of the standardized incidence-rate ratio, making weights proportional to person-time of the unexposed group . ir deaths smokes pyears, by(age) estandard

Create a variable that is always equal to 1 . generate conswgt = 1

Perform stratified analysis of the standardized incidence-rate ratio, weighting each age category equally . ir deaths smokes pyears, by(age) standard(conswgt) ---------------------------------------------------------------------------

Video example

Incidence-rate ratios calculator

Stored results

ir and iri store the following in r():

Scalars r(p) one-sided p-value r(ird) incidence-rate difference r(lb_ird) lower bound of CI for ird r(ub_ird) upper bound of CI for ird r(irr) incidence-rate ratio r(lb_irr) lower bound of CI for irr r(ub_irr) upper bound of CI for irr r(afe) attributable (prev.) fraction among exposed r(lb_afe) lower bound of CI for afe r(ub_afe) upper bound of CI for afe r(afp) attributable fraction for the population r(crude) crude estimate (ir only) r(lb_crude) lower bound of CI for crude r(ub_crude) upper bound of CI for crude r(pooled) pooled estimate (ir only) r(lb_pooled) lower bound of CI for pooled r(ub_pooled) upper bound of CI for pooled r(chi2_mh) Mantel-Haenszel homogeneity chi-squared (ir only) r(chi2_p) pooled homogeneity chi-squared r(df) degrees of freedom (ir only)


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