Re: [R] Formula of power.t.test

[Uwe Ligges]

Xiaorong Chen wrote:

Dear Sir or Madam,

What is the formula for power.t.test(delta=delta, sd=segma, sig.level=0.05, 
power=0.8, type="one.sample", alternative="one.sided")$n?
See the code of power.t.test by just typing the name of that function 
into the console:

  power.t.test

and you'll easily see that the code collapses in your case to:

  tsample <- 1
  tside <- 1
  p.body <- quote({
    nu <- (n - 1) * tsample
    pt(qt(sig.level/tside, nu, lower = FALSE),
      nu, ncp = sqrt(n/tsample) * delta/sd, lower = FALSE)
  })
  n <- uniroot(function(n) eval(p.body) - power, c(2, 1e+07))$root
Uwe Ligges


Thank you very much for the help!

Best,

Xiaorong

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