It seems to me that a transformation is in order since [0,1] can't possibly contain a normal distribution without cutting off both tails.
On Mon, 12 Jul 2004, Rolf Turner wrote: > > Darren Shaw wrote: > > > this may be a simple question - but i would appreciate any thoughts > > > > does anyone know how you would get one lower and one upper confidence > > interval for a set of data that consists of proportions. i.e. taking a > > usual confidence interval for normal data would result in the lower > > confidence interval being negative - which is not possible given the data > > (which is constrained between 0 and 1) > > > > i can see how you calculate a upper and lower confidence interval for a > > single proportion, but not for a set of proportions > > > (1) Your question appears to be a bit ``off topic''. I.e. it is > really about statistical methodology, rather than about how to > implement methodology in R. > > (2) You need to make the scenario clearer. What do your data > actually consist of? What are you assuming? > > The only reasonable scenario that springs to mind (perhaps this is > merely indicative of poverty of imagination on my part) is that you > have a number of ***independent*** samples, each yielding a sample > proportion, and each coming from the same population (or at least > from populations having the same population proportion ``p''. I.e. > you have p.hat_1, ..., p.hat_n and from these you wish to calculate a > confidence interval for p. > > You need to know the sample ***sizes*** for each sample. If you > don't, you're screwed. Full stop. There is absolutely nothing > sensible you can do. If you ***do*** know the sample sizes (say k_1, > ..., k_n) then the problem is trivial. > > You have p.hat_j = x_j/k_j for j = 1, ..., n. > > Let x = x_1 + ... + x_n and k = k_1 + ... + k_n. > > Form p.hat = x/k. (I.e. you ***really*** just have one big > happy sample.) Then calculate the confidence interval for p > in the usual way: > > p.hat +/- (z-value) * sqrt(p.hat * (1 - p.hat)/k) > > If this is not the scenario with which you need to cope, then > you'll have to explain what that scenario actually is. > > cheers, > > Rolf Turner > [EMAIL PROTECTED] > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > -- Clint Bowman INTERNET: [EMAIL PROTECTED] Air Quality Modeler INTERNET: [EMAIL PROTECTED] Department of Ecology VOICE: (360) 407-6815 PO Box 47600 FAX: (360) 407-7534 Olympia, WA 98504-7600 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
