# R/pwr.t.test.R In pwr: Basic Functions for Power Analysis

```"pwr.t.test" <-
function (n = NULL, d = NULL, sig.level = 0.05, power = NULL,
type = c("two.sample", "one.sample", "paired"), alternative = c("two.sided",
"less","greater"))
{
if (sum(sapply(list(n, d, power, sig.level), is.null)) !=
1)
stop("exactly one of n, d, power, and sig.level must be NULL")
if (!is.null(sig.level) && !is.numeric(sig.level) || any(0 >
sig.level | sig.level > 1))
stop(sQuote("sig.level"), " must be numeric in [0, 1]")
if (!is.null(power) && !is.numeric(power) || any(0 > power |
power > 1))
stop(sQuote("power"), " must be numeric in [0, 1]")
type <- match.arg(type)
alternative <- match.arg(alternative)
tsample <- switch(type, one.sample = 1, two.sample = 2, paired = 1)
ttside<-switch(alternative, less = 1, two.sided = 2, greater=3)

tside <- switch(alternative, less = 1, two.sided = 2, greater =1)
if (tside == 2 && !is.null(d))
d <- abs(d)
if (ttside == 1) {
p.body <- quote({
nu <- (n - 1) * tsample
pt(qt(sig.level/tside, nu, lower = TRUE), nu, ncp = sqrt(n/tsample) *
d, lower = TRUE)
})
}
if (ttside == 2)  {
p.body <- quote({
nu <- (n - 1) * tsample
qu <- qt(sig.level/tside, nu, lower = FALSE)
pt(qu, nu, ncp = sqrt(n/tsample) * d, lower = FALSE) +
pt(-qu, nu, ncp = sqrt(n/tsample) * d, lower = TRUE)
})
}
if (ttside == 3) {
p.body <- quote({
nu <- (n - 1) * tsample
pt(qt(sig.level/tside, nu, lower = FALSE), nu, ncp = sqrt(n/tsample) *
d, lower = FALSE)
})
}

if (is.null(power))
power <- eval(p.body)
else if (is.null(n))
n <- uniroot(function(n) eval(p.body) - power, c(2 +
1e-10, 1e+09))\$root
else if (is.null(d)) {
if(ttside==2){       d <- uniroot(function(d) eval(p.body) - power, c(1e-07,
10))\$root}
if(ttside==1){       d <- uniroot(function(d) eval(p.body) - power, c(-10,
5))\$root}
if(ttside==3){       d <- uniroot(function(d) eval(p.body) - power, c(-5,
10))\$root}

}
else if (is.null(sig.level))
sig.level <- uniroot(function(sig.level) eval(p.body) -
power, c(1e-10, 1 - 1e-10))\$root
else stop("internal error")
NOTE <- switch(type, paired = "n is number of *pairs*", two.sample = "n is number in *each* group",
NULL)
METHOD <- paste(switch(type, one.sample = "One-sample", two.sample = "Two-sample",
paired = "Paired"), "t test power calculation")
structure(list(n = n, d = d, sig.level = sig.level, power = power,
alternative = alternative, note = NOTE, method = METHOD),
class = "power.htest")
}
```

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pwr documentation built on May 30, 2017, 5:37 a.m.