effx {Epi} | R Documentation |
The function calculates the effects of an exposure on a response, possibly stratified by a stratifying variable, and/or controlled for one or more confounding variables.
effx( response, type = "metric", fup = NULL, exposure, strata = NULL, control = NULL, weights = NULL, alpha = 0.05, base = 1, digits = 3, data = NULL )
response |
The response variable - must be numeric |
type |
The type of responsetype - must be one of "metric",
"binary", "failure", or "count" |
fup |
The fup variable contains the follow-up time for a
failure response |
exposure |
The exposure variable can be numeric or a factor |
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. |
weights |
Frequency weights for binary response only |
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 |
The function is a wrapper for glm. Effects are calculated as differences in means for a metric response, odds ratios for a binary response, and rate ratios for a failure or count response.
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.
comp1 |
Effects of exposure |
comp2 |
Tests of significance |
Michael Hills
www.mhills.pwp.blueyonder.co.uk
library(Epi) data(births) births$hyp <- factor(births$hyp,labels=c("normal","hyper")) births$sex <- factor(births$sex,labels=c("M","F")) # bweight is the birth weight of the baby in gms, and is a metric # response (the default) # effect of hypertension on birth weight effx(bweight,exposure=hyp,data=births) # effect of hypertension on birth weight stratified by sex effx(bweight,exposure=hyp,strata=sex,data=births) # effect of hypertension on birth weight controlled for sex effx(bweight,exposure=hyp,control=sex,data=births) # effect of gestation time on birth weight effx(bweight,exposure=gestwks,data=births) # effect of gestation time on birth weight stratified by sex effx(bweight,exposure=gestwks,strata=sex,data=births) # effect of gestation time on birth weight controlled for sex effx(bweight,exposure=gestwks,control=sex,data=births) # lowbw is a binary response coded 1 for low birth weight and 0 otherwise # effect of hypertension on low birth weight effx(lowbw,type="binary",exposure=hyp,data=births) # etc.