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- # Write function
- t.test2 <- function(m1,m2,s1,s2,n1,n2,m0=0,equal.variance=FALSE)
- {
- if( equal.variance==FALSE )
- {
- se <- sqrt( (s1^2/n1) + (s2^2/n2) )
- # welch-satterthwaite df
- df <- ( (s1^2/n1 + s2^2/n2)^2 )/( (s1^2/n1)^2/(n1-1) + (s2^2/n2)^2/(n2-1) )
- } else
- {
- # pooled standard deviation, scaled by the sample sizes
- se <- sqrt( (1/n1 + 1/n2) * ((n1-1)*s1^2 + (n2-1)*s2^2)/(n1+n2-2) )
- df <- n1+n2-2
- }
- t <- (m1-m2-m0)/se
- dat <- c(m1-m2, se, t, 2*pt(-abs(t),df))
- names(dat) <- c("Difference of means", "Std Error", "t", "p-value")
- return(dat)
- }
- # Calculate t-statistic and p-value
- t.test2(m1=37.33, m2=39.65, s1=13.40, s2=15.91, n1=23,n2=32,
- equal.variance = FALSE)
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