Calculate the "phi coefficient" between two binary variables

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Description

The phicoef function calculates the "phi coefficient" between two binary variables.

Usage

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phicoef(x, y=NULL)

Arguments

x, y

Two logical vectors of the same length. If y is not supplied, x must be a 2x2 integer matrix (or an integer vector of length 4) representing the contingency table of two binary variables.

Value

The "phi coefficient" between the two binary variables. This is a single numeric value ranging from -1 to +1.

Author(s)

H. Pag├Ęs

References

http://en.wikipedia.org/wiki/Phi_coefficient

Examples

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set.seed(33)
x <- sample(c(TRUE, FALSE), 100, replace=TRUE)
y <- sample(c(TRUE, FALSE), 100, replace=TRUE)
phicoef(x, y)
phicoef(rep(x, 10), c(rep(x, 9), y))

stopifnot(phicoef(table(x, y)) == phicoef(x, y))
stopifnot(phicoef(y, x) == phicoef(x, y))
stopifnot(phicoef(x, !y) == - phicoef(x, y))
stopifnot(phicoef(x, x) == 1)