spooledfcalc: Calculates the degrees of freedom and the pooled variation...

In dusadrian/statistics: Miscellanea Functions For an Intro Stats Class

Calculates the degrees of freedom and the pooled variation for a t test

Description

The function dfcalc is used only for two samples t test, when the group variations are NOT equal. For small and independent samples, and unknown but equal population variances, the variances of the two samples are used. As the sample variances are never equal, this function calculates their pooled variance based on the two standard deviations and their respective sample sizes.

Usage

dfcalc(x, y, n1, n2)
spooled(x, y, n1, n2)

Arguments

x	The values of the standard deviation for the first group
y	The values of the standard deviation for the second group
n1	Size of the first group
n2	Size of the second group

Author(s)

Adrian Dusa

Examples

group1 <- c(13, 14,  9, 12,  8, 10,  5, 10,  9, 12, 16)
group2 <- c(16, 18, 11, 19, 14, 17, 13, 16, 17, 18, 22, 12)
sd1 <- sd(group1)
sd2 <- sd(group2)
n1 <- length(group1)
n2 <- length(group2)

# more direct
dfcalc(group1, group2)

# if the standard deviations and group sizes are known
dfcalc(sd1, sd2, n1, n2)

# the pooled standard deviation
spooled(sd1, sd2, n1, n2)

# more direct
spooled(group1, group2)

dusadrian/statistics documentation built on July 31, 2024, 1:05 a.m.