Re: [R] T-test to check equality, unable to interpret the results.

2009-09-18 Thread Greg Snow
It appears that you have a fundamental misunderstanding of what p-values do and do not say (though this misunderstanding is commom). The following article addresses this issue and could help with a better understanding: Murdock, D, Tsai, Y, and Adcock, J (2008) _P-Values are Random

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-18 Thread Greg Snow
Rolf, I no longer claim to be young, the naïve part is still up for debate, but I find that restricting the null to only include = to be more confusing than to have it include the inequality. To have the alternative be and the null be = implies that we are working on the assumption

[R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Robert Hall
Hi, I have the precision values of a system on two different data sets. The snippets of these results are as shown: sample1: (total 194 samples) 0.600238 0.800119 0.600238 0.200030 0.600238 ... ... sample2: (total 188 samples) 0.8001 0.2000 0.8001 0.

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Erik Iverson
Robert, We unfortunately do not have enough information to help you interpret the results, and this is not really an R question at all, but general statistical advice. You will probably have much better understanding and confidence in your results by consulting a local statistical consultant

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Steve Lianoglou
Hi, I was just going to send this when I saw Erik's post. He's right -- we can't say anything about your data, but we can say something about using a t-test. I'm not a real statistician, so this answer isn't very rigorous, but might be helpful. On Sep 16, 2009, at 2:55 PM, Robert Hall

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Bert Gunter
I am loathe to expound basic statistics here ... but, at the considerable risk of pedantry, I must note that Steve's reply below contains fundamental errors, which I feel should not be left on this list unremarked: t-tests do **not** test for differences in **sample** means; they test for

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Rolf Turner
On 17/09/2009, at 8:06 AM, Bert Gunter wrote: snip Furthermore, the null can be other than equality -- e.g. that the mean of the first population is less than the second. snip QUIBBLE: Some elementary texts will indeed state the null hypothesis as ``mu_1 = mu_2'' when

[R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Robert Hall
Hi, I have the precision values of a system on two different data sets. The snippets of these results are as shown: sample1: (total 194 samples) 0.600238 0.800119 0.600238 0.200030 0.600238 ... ... sample2: (total 188 samples) 0.8001 0.2000 0.8001 0.

Re: [R] T-test to check equality, unable to interpret the results.

2009-09-16 Thread Steve Lianoglou
Hi Bert, On Sep 16, 2009, at 4:06 PM, Bert Gunter wrote: snip Finally, statistically different is a meaningless phrase. I'm not sure if you're quoting that to point out something in particular you're taking exception to, but I never said that. I did mention statistical significance with