Thanks for your help RKoenker I want to deal with the problem through bootstrap.so I can get p-value and T-statistics. Do you think so? -- View this message in context: http://r.789695.n4.nabble.com/Question-of-Quantile-Regression-for-Longitudinal-Data-tp883458p3001875.html Sent from the R help mailing list archive at Nabble.com.