GenABEL (version 1.8-0)

ztransform: Transformation to standard Normal

Description

Transformation of a variable or residuals from GLM analysis to standard Normal.

Usage

ztransform(formula,data,family=gaussian)

Arguments

formula

GLM formula for the variable to be transformed, or just the variable

data

data.frame or gwaa.data object containing the data

family

GLM family

Value

Vector containing transformed variable, distributed as standard normal.

Details

Transformation to normality generates a variable which has mean zero and variance of one. If formula used, residuals from regression model are scaled to standard Normal.

See Also

ztransform

Examples

	# uniformly distributed variable
	x <- round(runif(200)*100)
	# get 7 missing values
	x[round(runif(7,min=1,max=100))] <- NA
	# Z-transform
	y0 <- ztransform(x)
	# Rank-transform to normality
	y1 <- rntransform(x)
	# test normality of the original and transformed var
	shapiro.test(x)
	shapiro.test(y0)
	shapiro.test(y1)
	# plot histogram
	par(mfcol=c(3,1))
	hist(x)
	hist(y0)
	hist(y1)
	# tests with genetic data
	require(GenABEL.data)
	data(srdta)
	Zqt1 <- ztransform(qt1,srdta)
	Zqt1sexA <- ztransform(qt1~sex,srdta)