Re: One tailed vs. Two tailed test

- I finally get back to this topic - On Fri, 16 Mar 2001 23:40:07 GMT, [EMAIL PROTECTED] (Jerry Dallal) wrote: > Rich Ulrich ([EMAIL PROTECTED]) wrote: > > : Notice, you can take out a 0.1% test and leave the main > : test as 4.9%, which is not effectively different from 5%. > > I've no pro

Re: One tailed vs. Two tailed test

On 16 Mar 2001 20:32:40 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: [ ... ] > seems to me when you fold over (say) a t distribution ... you don't have a > t distribution anymore ... mighten you have a chi square if before you fold > it over you square the values? [ ... snip, rest ] You ar

Re: One tailed vs. Two tailed test

On Fri, 16 Mar 2001 23:40:07 -, [EMAIL PROTECTED] (Jerry Dallal) wrote: >FWIW, for large samples, 0.1% in the unexpected tail >corresponds to a t statistic of 3.09. I'd love to >be a fly on the wall while someone is explaining to >a client why that t = 3.00 is non-significant! :-) What

Re: One tailed vs. Two tailed test

At 04:14 PM 3/16/01 -0500, Rich Ulrich wrote: >Sides? Tails? > >There are hypotheses that are one- or two-sided. >There are distributions (like the t) that are sometimes >folded over, in order report "two tails" worth of p-level >for the amount of the extreme. seems to me when you fold over (s

Re: One tailed vs. Two tailed test

Rich Ulrich ([EMAIL PROTECTED]) wrote: : Notice, you can take out a 0.1% test and leave the main : test as 4.9%, which is not effectively different from 5%. I've no problem with having different probabilities in the two tails as long as they're specified up front. I say so on my web page abo

Re: One tailed vs. Two tailed test

Sides? Tails? There are hypotheses that are one- or two-sided. There are distributions (like the t) that are sometimes folded over, in order report "two tails" worth of p-level for the amount of the extreme. I don't like to write about these, because it is so easy to be careless and write it

Re: One tailed vs. Two tailed test

I've thought about your proposal. Pages of mathematics with sups over composite parameter spaces reduce to this: The two-stage procedure is equivalent to a two-sided test. That is, from his/her behavior, it would be impossible to tell whether someone was acting according to your proposed two-stag

Re: One tailed vs. Two tailed test

I agree that it's the detail about which we disagree! However, one detail is pretty important - I still think you are confusing the trial and the statistical test. The same confusion is shown on the web site. I agree totally that if the treatment appears to be significantly worse than the control

Re: One tailed vs. Two tailed test

jim clark wrote: > The chi^2 distribution is equivalent to the z distribution > "folded over" so that both negative and positive tails of z are > in the upper (i.e., positive) tail of chi^2. The same > relationship holds between t and F. As we saw recently on this > (or another stats list), ther

Re: One tailed vs. Two tailed test

We don't really disagree. Any apparent disagreement is probably due to the abbreviated kind of discussion that takes place in Usenet. See http://www.tufts.edu/~gdallal/onesided.htm Alan McLean ([EMAIL PROTECTED]) wrote: > My point however is still true - that the person who receives > the contr

Re: One tailed vs. Two tailed test

Jerry Dallal wrote: > > Alan McLean ([EMAIL PROTECTED]) wrote: > > : There is certainly an argument that when trialling a new treatment (I > : initially used the word 'testing' here, but figure that it may be > : confused with the statistical test of the resultant data) it is > : presumably expe

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, RD <[EMAIL PROTECTED]> wrote: >On 13 Mar 2001 16:32:15 -0500, [EMAIL PROTECTED] (Herman >Rubin) wrote: >>In article <[EMAIL PROTECTED]>, >>RD <[EMAIL PROTECTED]> wrote: >>>On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: 1. some test

Re: One tailed vs. Two tailed test

Alan McLean ([EMAIL PROTECTED]) wrote: : There is certainly an argument that when trialling a new treatment (I : initially used the word 'testing' here, but figure that it may be : confused with the statistical test of the resultant data) it is : presumably expected to work. Consequently, if a pe

Re: One tailed vs. Two tailed test

dennis roberts ([EMAIL PROTECTED]) wrote: : it would only be unethical if a better alternative were available ... or : even a possibly better alternative were available ... and the investigator : or the one making the decision to give or not to give ... KNOWS this ... : AND HAS the ability to

Re: One tailed vs. Two tailed test

As we saw recently on this > (or another stats list), there is much confusion between > "one-tailed" in the sense of a directional test (which concerns > the direction of differences or correlations) and "one-tailed" in > the narrower sense of tail of distribution (e.g., chi^2). These > uses are

Re: One tailed vs. Two tailed test

Apart from making the observation that there are many applications of tests that do not involve ethical considerations, I am not at all clear how this example relates to one or two tailed testing. There is certainly an argument that when trialling a new treatment (I initially used the word 'testi

Re: One tailed vs. Two tailed test

Hi On 13 Mar 2001, dennis roberts wrote: > i give a survey and ... have categorized respondents into male and females > ... and also into science major and non science majors ... and find a data > table like: > non science science > C1 C2Total > M 1 24

Re: One tailed vs. Two tailed test

On 13 Mar 2001 14:23:04 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: >well, help me out a bit > >i give a survey and ... have categorized respondents into male and females >... and also into science major and non science majors ... and find a data >table like: > >MTB > chisquare c1 c2 > >Ch

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, Alan McLean <[EMAIL PROTECTED]> wrote: >Will Hopkins wrote: >> Responses to various folks. And to everyone touchy about one-tailed >> tests, let me make it quite clear that I am only promoting them as a >> way of making a sensible statement about probability. A t

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, Alan McLean <[EMAIL PROTECTED]> wrote: >[EMAIL PROTECTED] wrote: >> More importantly, I would say: DON'T DO TESTS. Instead, try to find >> models that you would be prepared to use to predict the response >> in as-yet untried circumstances. >> -- >Hypothesis tes

Re: One tailed vs. Two tailed test

On 13 Mar 2001 16:32:15 -0500, [EMAIL PROTECTED] (Herman Rubin) wrote: >In article <[EMAIL PROTECTED]>, >RD <[EMAIL PROTECTED]> wrote: >>On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: > >>>1. some test statistics are naturally (the way they work anyway) ONE sided >>>wi

Re: One tailed vs. Two tailed test

At 03:39 PM 3/14/01 +, Jerry Dallal wrote: >It wasn't ironically and has nothing to do with 5%. As Marvin Zelen >has pointed out, one-tailed tests are unethical from a human >subjects perspective because they state that the difference can go >in only one direction (we can argue about tests t

Re: One tailed vs. Two tailed test

In article , Will Hopkins <[EMAIL PROTECTED]> wrote: >Responses to various folks. And to everyone touchy about one-tailed >tests, let me make it quite clear that I am only promoting them as a >way of making a sensible statement about probability. A two-t

Re: One tailed vs. Two tailed test

Jerry Dallal wrote: > > It wasn't ironically and has nothing to do with 5%. As Marvin Zelen > has pointed out, one-tailed tests are unethical from a human > subjects perspective because they state that the difference can go > in only one direction (we can argue about tests that are similar on

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, [EMAIL PROTECTED] (Alan McLean) writes: >[EMAIL PROTECTED] wrote: >> >> More importantly, I would say: DON'T DO TESTS. Instead, try to find >> models that you would be prepared to use to predict the response >> in as-yet untried circumstances. >> -- > >Hyp

Re: One tailed vs. Two tailed test

Will Hopkins wrote: > > Jerry Dallal wrote, ironically: > >If you're doing a 1 tailed test, why test at all? Just switch from > >standard treatment to the new one. Can't do any harm. Every field > >is littered with examples where one-tailed tests would have led to > >disasters (harmful treatmen

Re: One tailed vs. Two tailed test

Thanks for your e-mail (which arrived much later than your post to the newsgroup). I've already posted an apology and half-retraction for saying something I didn't really mean! -- Ewart J.E.H.Shaw [Ewart Shaw][EMAIL PROTECTED] TEL: +44 2476 523069 Department of Statistic

Re: One tailed vs. Two tailed test

[EMAIL PROTECTED] wrote: > > > More importantly, I would say: DON'T DO TESTS. Instead, try to find > models that you would be prepared to use to predict the response > in as-yet untried circumstances. > -- Hypothesis testing is simply one useful method of identifying 'models that you would be

Re: One tailed vs. Two tailed test

On 13 Mar 2001 21:18:38 GMT, [EMAIL PROTECTED] () wrote: >In article <[EMAIL PROTECTED]>, > RD <[EMAIL PROTECTED]> writes: >>On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: >> >>>1. some test statistics are naturally (the way they work anyway) ONE sided >>>with res

Re: One tailed vs. Two tailed test

Responses to various folks. And to everyone touchy about one-tailed tests, let me make it quite clear that I am only promoting them as a way of making a sensible statement about probability. A two-tailed p value has no real meaning, because no real effects are ever null. A one-tailed p valu

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, RD <[EMAIL PROTECTED]> writes: >On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: > >>1. some test statistics are naturally (the way they work anyway) ONE sided >>with respect to retain/reject decisions >> >>example: chi square test f

Re: One tailed vs. Two tailed test

In article <[EMAIL PROTECTED]>, RD <[EMAIL PROTECTED]> wrote: >On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: >>1. some test statistics are naturally (the way they work anyway) ONE sided >>with respect to retain/reject decisions >>example: chi square test for independ

Re: One tailed vs. Two tailed test

well, help me out a bit i give a survey and ... have categorized respondents into male and females ... and also into science major and non science majors ... and find a data table like: MTB > chisquare c1 c2 Chi-Square Test: C1, C2 Expected counts are printed below observed counts

Re: One tailed vs. Two tailed test

On 13 Mar 2001 07:12:33 -0800, [EMAIL PROTECTED] (dennis roberts) wrote: >1. some test statistics are naturally (the way they work anyway) ONE sided >with respect to retain/reject decisions > >example: chi square test for independence ... we reject ONLY when chi >square is LARGER than some CV .

Re: One tailed vs. Two tailed test

Will Hopkins wrote: > > At 7:34 PM + 12/3/01, Jerry Dallal wrote: > >Don't do one-tailed tests. > > If you are going to do any tests, it makes more sense to one-tailed > tests. If you're doing a 1 tailed test, why test at all? Just switch from standard treatment to the new one. Can't do

Re: One tailed vs. Two tailed test

In article , Will Hopkins <[EMAIL PROTECTED]> wrote: >At 7:34 PM + 12/3/01, Jerry Dallal wrote: >>Don't do one-tailed tests. >If you are going to do any tests, it makes more sense to one-tailed >tests. The resulting p value actually means something th

Re: One tailed vs. Two tailed test

dennis roberts wrote: > > we have to first separate out 2 things: > > 1. some test statistics are naturally (the way they work anyway) ONE sided > with respect to retain/reject decisions > > example: chi square test for independence ... we reject ONLY when chi > square is LARGER than some CV

Re: One tailed vs. Two tailed test

we have to first separate out 2 things: 1. some test statistics are naturally (the way they work anyway) ONE sided with respect to retain/reject decisions example: chi square test for independence ... we reject ONLY when chi square is LARGER than some CV ... to put a CV at the lower end of the

Re: One tailed vs. Two tailed test

On Tue, 13 Mar 2001, Will Hopkins wrote in part: > Example: you observe an effect of +5.3 units, one-tailed p = 0.04. > Therefore there is a probability of 0.04 that the true value is less > than zero. Sorry, that's incorrect. The probability is 0.04 that you would find an effect as large a

Re: One tailed vs. Two tailed test

At 7:34 PM + 12/3/01, Jerry Dallal wrote: >Don't do one-tailed tests. If you are going to do any tests, it makes more sense to one-tailed tests. The resulting p value actually means something that folks can understand: it's the probability the true value of the effect is opposite to what

Re: One tailed vs. Two tailed test

auda wrote: > > Hi, all, > We are testing a group of subjects on their performance in two different > conditions (say, A and B), and we are testing them individually. We have an > alternative hypothesis that reaction time in condition A should be longer > than in condition B, so we perform a one-

Re: One tailed vs. Two tailed test

auda wrote: > > Hi, all, > We are testing a group of subjects on their performance in two different > conditions (say, A and B), and we are testing them individually. We have an > alternative hypothesis that reaction time in condition A should be longer > than in condition B, so we perform a one-

One tailed vs. Two tailed test

Hi, all, We are testing a group of subjects on their performance in two different conditions (say, A and B), and we are testing them individually. We have an alternative hypothesis that reaction time in condition A should be longer than in condition B, so we perform a one-tailed t test. However, f