Why can't I just use Log odds? Does the standard error of the logs score depend on a similar chisq assumption?
On Sat, 9 Oct 2004, Dan Bolser wrote: > >I have the following contingency table > >dat <- matrix(c(1,506,13714,878702),nr=2) > >And I want to test if their is an association between events > >A:{a,not(a)} and B:{b,not(b)} > > | b | not(b) | >--------+-----+--------+ > a | 1 | 13714 | >--------+-----+--------+ > not(a) | 506 | 878702 | >--------+-----+--------+ > >I am worried that prop.test and chisq.test are not valid given the low >counts and low probabilites associated with 'sucess' in each category. > >Is it safe to use them, and what is the alternative? (given that >fisher.test can't handle this data... hold the phone... > >I just found fisher.test can handle this data if the test is one-tailed >and not two-tailed. > >I don't understand the difference between chisq.test, prop.test and >fisher.test when the hybrid=1 option is used for the fisher.test. > >I was using the binomial distribution to test the 'extremity' of the >observed data, but now I think I know why that is inapropriate, however, >with the binomial (and its approximation) at least I know what I am >doing. And I can do it in perl easily... > >Generally, how should I calculate fisher.test in perl (i.e. what are its >principles). When is it safe to approximate fisher to chisq? > >I cannot get insight into this problem... > >How come if I do... > >dat <- matrix(c(50,60,100,100),nr=2) > >prop.test(dat)$p.value >chisq.test(dat)$p.value >fisher.test(dat)$p.value > >I get > >[1] 0.5173269 >[1] 0.5173269 >[1] 0.4771358 > >When I looked at the binomial distribution and the normal approximation >thereof with similar counts I never had a p-value difference > 0.004 > >I am so fed up with this problem :( > >______________________________________________ >[EMAIL PROTECTED] mailing list >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html