chi-square test
if you print "chisq.test()" you'll see when this warning message appears (i.e., if any expected count is less than 5, in which case it is known that the approximation to the Chi-squared distribution may not be adequate). Alternatively, you could simulate to approximate the reference distribution of the statistic and obtain an estimation of the p-value using: chisq.test(matrix(c(20.1, 18.5, 2.6, 32.9, 23.5, 5.4), nc = 2), simulate.p.value = TRUE) I hope it helps. Best, Dimitris p.s., you should send this message to r-help and not r-devel. ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/16/336899 Fax: +32/16/337015 Web: http://www.med.kuleuven.ac.be/biostat/ http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm ----- Original Message ----- From: "Benjamin Chan [BRE]" <Benjamin.Chan@inet.polyu.edu.hk> To: <r-devel@stat.math.ethz.ch> Sent: Tuesday, April 19, 2005 10:47 AM Subject: [Rd] chi-square test
a warning message appears when i use the chisq.test ,but it doesnt appear everytime, why? "Warning message: Chi-squared approximation may be incorrect in: chisq.test(matrix(c(20.1, 18.5, 2.6, 32.9, 23.5, 5.4), nc = 2)) " why does the warning message appear, please? Thank you very much here is the data which I have tried appear and not appear warning message have warning message (1.3,4.9,12.6,10.5,5.5,6.5,4.7,9.8,10.3,23.2,7.3,6.6) (13.8,8.4,8.7,10.4,25.5,28.7,2.5,5.1) (20.1,18.5,2.6,32.9,23.5,5.4) doesnt have warning message (32.7,8.6,2561.5,2726.5) (44.4,17.4,2561.5,2726.5) (44.4,17.4,32.7,8.6) (13.9,22.3,5.1,17.4,32.3,12) (8.1,5.2,13.8,11.5,2.6,15.8,15.5,9.6,6.7,14.2) (13.9,17.4,22.3,1740,2230,1390) [[alternative HTML version deleted]]
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