alpha {MiscPsycho} | R Documentation |
Computes Cronbach's alpha. This reduces to KR-20 when the columns of the data matrix are dichotomous.
alpha(...) ## Default S3 method: alpha(dat, ...) ## S3 method for class 'formula': alpha(formula, data, na.action, subset, ...)
formula |
an object of class "formula" (or one that can be
coerced to that class): a symbolic description of the model
to be fitted. The details of model specification are given
under Details . |
data |
an optional data frame, list or environment (or object
coercible by as.data.frame to a data frame) containing
the variables in the model. If not found in data , the
variables are taken from environment(formula) ,
typically the environment from which alpha is called. |
dat |
A data frame or matrix with item responses. Implemented only for the alpha.default method. |
na.action |
a function which indicates what should happen when the data
contain NA s. Defaults to getOption("na.action") . |
subset |
an optional vector specifying a subset of observations to be used. |
... |
Not implemented |
The conditional alpha is accesible via the summary
method for objects of class alpha
A list with class "alpha"
containing the following components:
alpha |
coefficient alpha |
numItems |
the number of test items used in the computation |
condAlpha |
The alpha that would be realized if the item were excluded |
Harold C. Doran
set.seed(1234) tmp <- data.frame(item1 = sample(c(0,1), 20, replace=TRUE), item2 = sample(c(0,1), 20, replace=TRUE), item3 = sample(c(0,1), 20, replace=TRUE),item4 = sample(c(0,1), 20, replace=TRUE),item5 = sample(c(0,1), 20, replace=TRUE)) ## Formula interface fm1 <- alpha(~ item1 + item2 + item3 + item4 + item5, data = tmp) summary(fm1) coef(fm1) ## Default interface fm1 <- alpha(tmp) summary(fm1)