# NOT RUN {
x <- 1:20
sd(x)/sqrt(length(x))
se(x)
# all return NA if missing values are not removed
x2 <- c(x,NA)
sd(x2)/sqrt(length(x2))
# Better if missing values are removed
se(x2,na.rm=FALSE)
sd(x2,na.rm=TRUE)/sqrt(length(x2[complete.cases(x2)]))
se(x2)
# }
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