In the case of the t.test, having the default be var.equal=TRUE is the right way to go. There is little to no power lost by using the welch test, and the assumption of equal variance can be difficult to assess. For this reason, many introductory text books have now banished the equal variance t-test from their chapters (e.g. Moore's The Basic Practice of Statistics).
Ian On Oct 25, 2010, at 4:05 PM, Albyn Jones wrote: > I don't know, the help file is uninformative. I'd guess the answer is > "the author wrote it that way". Other R functions like t.test include > similar unfortunate (to me) default choices, in that case > var.equal=FALSE (ie the Welch test) is the default. > > albyn > > On Mon, Oct 25, 2010 at 04:15:20PM -0500, Laura Chihara wrote: >> Yes, thank you for this reference. But according to >> this article, the score is better than continuity >> correction, so why is continuity correction the default >> with prop.test? >> >> -Laura >> >> On 10/25/2010 4:02 PM, Ralph O'Brien, PhD wrote: >>> I suggest: >>> >>> A. Agresti and B. A. Coull. Approximate is better than ”exact” for >>> interval estimation of binomial proportions. The American Statistician, >>> 52(2):119–126, 1998. >>> >>> >>> >>> >>> >>> >>> >>> On Mon, Oct 25, 2010 at 4:38 PM, Laura Chihara <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Hi, >>> >>> I have a question about prop.test in R: >>> >>> I teach students the score confidence >>> interval for proportions (also called >>> Wilson or Wilson score interval). >>> >>> prop.test(,..., correct=FALSE) gives this >>> interval. >>> >>> The default uses a continuity correction. >>> When should we use one over the other? >>> Is it worth going over this in class? Why >>> is correct=TRUE the default? >>> >>> Thanks for any pedagogical guidance here! >>> >>> -- Laura >>> >>> ******************************************* >>> Laura Chihara >>> Professor of Mathematics 507-222-4065 (office) >>> Dept of Mathematics 507-222-4312 (fax) >>> Carleton College >>> 1 North College Street >>> Northfield MN 55057 >>> >>> _______________________________________________ >>> [email protected] <mailto:[email protected]> >>> mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-sig-teaching >>> >>> >>> >>> >>> -- >>> Ralph O'Brien, PhD >>> Professor, Dept of Epidemiology and Biostatistics >>> Case Western Reserve University >>> Office: 216.368.1927 >>> Cell: 216.312.3203 >> >> -- >> ******************************************* >> Laura Chihara >> Professor of Mathematics 507-222-4065 (office) >> Dept of Mathematics 507-222-4312 (fax) >> Carleton College >> 1 North College Street >> Northfield MN 55057 >> >> _______________________________________________ >> [email protected] mailing list >> https://stat.ethz.ch/mailman/listinfo/r-sig-teaching >> > > -- > Albyn Jones > Reed College > [email protected] > > _______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-sig-teaching _______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-sig-teaching
