Hi, I am trying to create a power curve to show how the power of a t-test varies depending on the mean. Any ideas how I should go about this? Louisa _________________________________________________________________ [[alternative HTML version deleted]]
Louisa Hay wrote:> > Hi, > I am trying to create a power curve to show how the power of a t-test varies depending on the mean. Any ideas how I should go about this? > LouisaThe pt() function supports a non-centrality parameter, so you can do this calculation directly. For other situations where the non-null distribution isn't easy to work with, there's always simulation. Just simulate a large number of samples, and compute how many of them are rejected. Duncan Murdoch
On 4/14/2008 6:21 AM, Louisa Hay wrote:> > Hi, > I am trying to create a power curve to show how the power of a t-test varies depending on the mean. Any ideas how I should go about this? > LouisaSomething like this maybe? mydiffs <- seq(.05,1,.05) mypower <- vector("numeric", 20) for(i in 1:20){ mypower[i] <- power.t.test(n=100, sd=1, delta=mydiffs[i])$power } plot(mymeans, mypower, xlab="delta", ylab="Power", type="b") See ?power.t.test> _________________________________________________________________ > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.-- Chuck Cleland, Ph.D. NDRI, Inc. (www.ndri.org) 71 West 23rd Street, 8th floor New York, NY 10010 tel: (212) 845-4495 (Tu, Th) tel: (732) 512-0171 (M, W, F) fax: (917) 438-0894
On 4/14/2008 6:35 AM, Chuck Cleland wrote:> On 4/14/2008 6:21 AM, Louisa Hay wrote: >> >> Hi, >> I am trying to create a power curve to show how the power of a t-test varies depending on the mean. Any ideas how I should go about this? >> Louisa > > Something like this maybe? > > mydiffs <- seq(.05,1,.05) > > mypower <- vector("numeric", 20) > > for(i in 1:20){ > mypower[i] <- power.t.test(n=100, sd=1, delta=mydiffs[i])$power > } > > plot(mymeans, mypower, xlab="delta", ylab="Power", type="b")Sorry - that last line should be: plot(mydiffs, mypower, xlab="delta", ylab="Power", type="b")> See ?power.t.test > >> _________________________________________________________________ >> >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code.-- Chuck Cleland, Ph.D. NDRI, Inc. (www.ndri.org) 71 West 23rd Street, 8th floor New York, NY 10010 tel: (212) 845-4495 (Tu, Th) tel: (732) 512-0171 (M, W, F) fax: (917) 438-0894