effx.match {Epi}R Documentation

Function to calculate effects for individually matched case-control studies

Description

The function calculates the effects of an exposure on a response, possibly stratified by a stratifying variable, and/or controlled for one of more confounding variables.

Usage

effx.match(response,
exposure,
match,
strata=NULL,
control=NULL,
base=1,
digits=3,
alpha=0.05,
data=NULL) 

Arguments

response The response variable - must be numeric
exposure The exposure variable can be numeric or a factor
match The variable which identifies the matched sets
strata The strata stratifying variable - must be a factor
control The control variable(s). These are passed as a list if there are more than one of them.
base Baseline for the effects of a categorical exposure, default 1
digits Number of significant digits for the effects, default 3
alpha 1 - confidence level
data data refers to the data used to evaluate the function

Details

Effects are calculated odds ratios. The function is a wrapper for clogit, from the survival package. The k-1 effects for a categorical exposure with k levels are relative to a baseline which, by default, is the first level. The effect of a metric (quantitative) exposure is calculated per unit of exposure. The exposure variable can be numeric or a factor, but if it is an ordered factor the order will be ignored.

Value

comp1 Effects of exposure
comp2 Tests of significance

Warning

The function attaches the frame specified in the data= argument, so there is a possibility that a variable in the Global environment is masked by the attached frame. Watch out for this warning in the output!

Author(s)

Michael Hills

References

www.mhills.pwp.blueyonder.co.uk

Examples

library(Epi)
library(survival)
data(bdendo)

# d is the case-control variable, set is the matching variable.
# The variable est is a factor and refers to estrogen use (yes,no)
# The variable age is numeric and refers to estrogen use (yes,no)
# effect of est on the odds of being a case
effx.match(d,exposure=est,match=set,data=bdendo)
# effect of age on the odds of being a case
effx.match(d,exposure=age,match=set,data=bdendo)

[Package Epi version 0.9.0 Index]