ANOVA will give you an adjusted t-test. For example: fit<-lm(height~sex+age) summary(fit) Will give an age-adjusted t-test of the heights of men and women. John John Sorkin Chief Biostatistics and Informatics Univ. of Maryland School of Medicine Division of Gerontology and Geriatric Medicine jsor...@grecc.umaryland.edu -----Original Message----- From: Erik Iverson <er...@ccbr.umn.edu> To: <josef.kar...@phila.gov> Cc: <r-help@r-project.org>
Sent: 8/7/2010 4:24:35 PM Subject: Re: [R] basic question about t-test with adjusted p value On 08/07/2010 03:08 PM, josef.kar...@phila.gov wrote: > I have read the R manual and help archives, sorry but I'm still stuck. > > How would I do a t-test with an adjusted p-value? Please be more specific about what you mean by 'adjusted p-value'. See below... > > Suppose that I use t.test ( ) , with the function argument alternative = > "two.sided", and data such that degrees of freedom = 20. The function > calculates a t-statistic of 2.086, and p-value =0.05 > > How do I then adjust the p-value? My thought is to do > p.adjust (pt(2.086, df=20),"BH") > but that doesn't change anything (returns 0.975) A couple things here. 1) You can get the p-value returned from t.test by inspecting the object with ?str, and noting that it's stored in an element called p-value. So, p.val <- t.test(extra ~ group, data = sleep)$p.value assigns the p-value to an object called p.val. 2) You're calling p.adjust with a single p-value, so what kind of adjustment did you have in mind? You would normally be adjusting p-values because of a multiple comparison issue (i.e., multiple tests performed). You'd pass p.adjust the *vector* of p-values, and a method to adjust them by. Your vector is of length 1, so in p.adjust's opinion, there is nothing to adjust for. So, what do *you* mean by 'adjusted p-value'? `Why are you looking to adjust?` is another way of stating that. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Confidentiality Statement: This email message, including any attachments, is for th...{{dropped:6}} ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
