sm (version 2.0-2)

sm.density.compare: Comparison of univariate density estimates

Description

This function allows a set of univariate density estimates to be compared, both graphically and formally in a bootstrap hypothesis test of equality.

Usage

sm.density.compare(x, group, h=NA, model="none", test=TRUE,
                   nboot=100, monitor=TRUE, ...)

Arguments

x

a vector of data.

group

a vector of group labels.

h

the smoothing parameter to be used in the construction of each density estimate. Notice that the same smoothing parameter is used for each group. If this value is omitted, the mean of the normal optimal values for the different groups is used.

model

the default value is "none" which restricts comparison to plotting only. The alternative value "equal" can produce a bootstrap hypothesis test of equality and the display of an appropriate reference band.

test

a logical flag controlling the production of a bootstrap test of equality.

band

a logical flag controlling the production of a reference band for equality. A band will be produced only in the case of two groups.

nboot

the number of bootstrap simulations.

monitor

a logical flag controlling the printing of the iteration numbers during the bootstrap test.

...

additional sm.options or graphical parameters.

Value

• When model is set to "none", nothing is returned. When "model" is set to "equal", a list containing the smoothing parameter and the p-value of the test is returned. When band takes the value TRUE, and there are only two groups to compare, the list contains in addition the upper and lower end-points of the reference band for equality.

Side Effects

none.

Details

see Section 6.2 of the reference below.

References

Bowman, A.W. and Azzalini, A. (1997). Applied Smoothing Techniques for Data Analysis: the Kernel Approach with S-Plus Illustrations. Oxford University Press, Oxford.

See Also

sm.density, sm.ancova

Examples

y <- rnorm(100)
g <- rep(1:2, rep(50,2))
sm.density.compare(y, g, model="equal")