Zembower, Kevin
2007-Nov-07 19:53 UTC
[R] Homework help: t test hypothesis testing with summarized data?
Is this how a t hypothesis test is done when I don't have the actual data, but just the summarized statistics:> #Homework 9.2.6 [1] > n<-31 > xbar<-3.10 > s_x<-1.469 > m<-57 > ybar<-2.43 > s_y<-1.35 > s_pooled<- (((n-1)*s_x^2) + ((m-1)*s_y^2)) / (n + m - 2) > s_pooled[1] 1.939521> t_obs <- (xbar - ybar) / (s_pooled * (sqrt(1/n + 1/m))) > t_obs[1] 1.547951> qt(c(.025, .975), n+m-2)[1] -1.987934 1.987934> # Therefore, fail to reject H0 at the 0.05 level of significance >Or am I again overlooking a canned procedure or an easier calculation using the t distribution. Thank you for your continued advice and help. -Kevin [1] An Introduction to Mathematical Statistics and its Applications, fourth ed., Larsen and Marx. Kevin Zembower Internet Services Group manager Center for Communication Programs Bloomberg School of Public Health Johns Hopkins University 111 Market Place, Suite 310 Baltimore, Maryland 21202 410-659-6139
Peter Dalgaard
2007-Nov-07 23:50 UTC
[R] Homework help: t test hypothesis testing with summarized data?
Zembower, Kevin wrote:> Is this how a t hypothesis test is done when I don't have the actual > data, but just the summarized statistics: > >> #Homework 9.2.6 [1] >> n<-31 >> xbar<-3.10 >> s_x<-1.469 >> m<-57 >> ybar<-2.43 >> s_y<-1.35 >> s_pooled<- (((n-1)*s_x^2) + ((m-1)*s_y^2)) / (n + m - 2) >> s_pooled >> > [1] 1.939521 > >> t_obs <- (xbar - ybar) / (s_pooled * (sqrt(1/n + 1/m))) >> t_obs >> > [1] 1.547951 > >> qt(c(.025, .975), n+m-2) >> > [1] -1.987934 1.987934 > >> # Therefore, fail to reject H0 at the 0.05 level of significance >> >> > > Or am I again overlooking a canned procedure or an easier calculation > using the t distribution. >I don't know if someone told you last time, but there's an Internet code of honor about helping with homework.... Don't expect more than hints. You're on track but there's a mistake. Here's a way of testing your result: > x <- scale(rnorm(31))*1.469+3.10 > y <- scale(rnorm(57))*1.35+2.43 > t.test(x,y, var.equal=TRUE)> Thank you for your continued advice and help. > > -Kevin > > [1] An Introduction to Mathematical Statistics and its Applications, > fourth ed., Larsen and Marx. > > Kevin Zembower > Internet Services Group manager > Center for Communication Programs > Bloomberg School of Public Health > Johns Hopkins University > 111 Market Place, Suite 310 > Baltimore, Maryland 21202 > 410-659-6139 > > ______________________________________________ > R-help at 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. >-- O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907