Re: A question

2001-05-05 Thread Alan McLean
Thanks, Robert, and to anyone else who has kindly answered what I realised, belatedly, was a simple question (given that I was looking for the simple normal case.) Regards, Alan "Robert J. MacG. Dawson" wrote: > > Alan McLean wrote: > > > > Hi to all. > > > > Can anyone tell me what is the di

Re: A question

2001-05-04 Thread dennis roberts
well, i don't have the answer but, a quick simulation (when the ratio of variances is about 2) is as follows maybe this helps in some strange way === MTB > rand 1 c1-c25; SUBC> norm 100 5. MTB > rand 1 c26-c50; SUBC> norm 100 7.07. MTB > rstdev c1-c25, c51 MTB > rstdev c26-c50, c

Re: A question

2001-05-04 Thread Robert J. MacG. Dawson
Alan McLean wrote: > > Hi to all. > > Can anyone tell me what is the distribution of the ratio of sample > variances when the ratio of population vriances is not 1, but some > specified other number? *If* the population distributions are normal (and this is not a robust assumption -

Re: A question

2001-05-04 Thread Donald Burrill
On Fri, 4 May 2001, Alan McLean wrote: > Can anyone tell me what is the distribution of the ratio of sample > variances when the ratio of population variances is not 1, but some > specified other number? Depends. If the two samples on which the variances are based are _independent_, s^2(1)/s^2

A question

2001-05-03 Thread Alan McLean
Hi to all. Can anyone tell me what is the distribution of the ratio of sample variances when the ratio of population vriances is not 1, but some specified other number? I want to be able to calculate the probability of getting a sample ratio of 1 when the population ratio is, say, 2. Many than

Re: A question on hypothesis testing wrt a factor in a GLM model.

2000-03-07 Thread Paul Y. Peng
Thank you for your reply, the only one I have got so far. "Donald F. Burrill" wrote: > > Looks to me like a simple typo. The null hypothesis is > H0: beta1 = beta2 = 0 > and I would attribute the "+" sign to a typing error ("+" is a shifted > "=" on most keyboards). You may be right

Re: A question on hypothesis testing wrt a factor in a GLM model.

2000-03-05 Thread Donald F. Burrill
Looks to me like a simple typo. The null hypothesis is H0: beta1 = beta2 = 0 and I would attribute the "+" sign to a typing error ("+" is a shifted "=" on most keyboards). While the _interpretation_ of non-zero estimates of the betas (should H0 be rejected) depends on the spec

A question on hypothesis testing wrt a factor in a GLM model.

2000-03-04 Thread Paul Y. Peng
Suppose that I have a factor with three levels A, B, and C. If it is used in a GLM model as a covariate, I will have two parameter beta1 and beta2 (assuming they are for level B and C). To test a statement "Any of the last two levels (either level B or level C) has a different effect on the respon