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
non science science
C1 C2 Total
M 1 24 43 67
32.98 34.02
F 2 39 22 61
30.02 30.98
Total 63 65 128
Chi-Sq = 2.444 + 2.368 +
2.684 + 2.601 = 10.097
DF = 1, P-Value = 0.001
when we evaluate THIS test ... with the chi square test statistic we use in
THIS case ... in what sense would this be considered to be a TWO tailed
test? would we still be using say ... the typical value of .05 to make a
decision to retain or reject? would we be asking the tester to look up both
lower and upper CVs from a chi square distribution with 1 df ... and really
ask him/her to consider rejecting if the obtained chi squared value is
smaller than the lower CV?
in this case ... minitab is finding the area ABOVE 10.097 in a chi square
distribution with 1 df ... and recording it as the P value ...
of course, in a simple hypothesis test for a single population mean ... like
Test of mu = 31 vs mu not = 31
Variable N Mean StDev SE Mean
C5 20 28.10 6.71 1.50
Variable 95.0% CI T P
C5 ( 24.96, 31.24) -1.93 0.068
the p value that is listed is found by taking the area TO THE LEFT of -1.93
and to the RIGHT of +1.93 in a t distribution with 19 df ... and adding
them together
At 08:50 PM 3/13/01 +0100, RD 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 independence ... we reject ONLY when chi
> >square is LARGER than some CV ... to put a CV at the lower end of the
> >relevant chi square distribution makes no sense
> >
>Hmm... do not want to start flame war but just can not go by such HUGE
>misconception about chi squared test.
>Now getting back to original question.
>Incidentally my opinion agrees with international harmonisation
>guidelines. Just dig FDA site to find them. There are half-page
>additional explanations why one tailed tests with 5% are unacceptable.
>The result you can not submit a drug for approval based on studies
>with one tailed 5% rate tests.
agreement with another position is not sufficient evidence to discard the
notion that one tailed tests can be legitimate in some cases
are you suggesting that the model for drug research is always correct?
>I am dermatologist not statistitian and all those questions seems
>obvious to me. I am disappointed.
>
>
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_________________________________________________________
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm
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