Hi.
I'm trying to calculate the weighted mean score of a quality of life measure (ovt) in patients with irritable bowel syndrome by their marital status (d7). This is a summary of the structure of the dataset: > str(sii.tesis) 'data.frame': 1063 obs. of 75 variables: $ id : int 51 52 53 54 55 56 57 58 59 60 ... $ stratum : Factor w/ 6 levels "MEst","MAcad",..: 1 4 NA 4 4 1 6 NA 4 4 ... $ expfc : num 22.8 17.1 NA 17.1 17.1 ... $ d6 : Factor w/ 3 levels "Estudiante","Profesor",..: 1 1 NA 1 1 1 3 NA 1 1 ... $ d7 : Factor w/ 6 levels "Soltero","Casado",..: 1 1 NA 1 1 1 1 NA 1 1 ... $ d7c : Factor w/ 2 levels "No estable","Estable": 1 1 NA 1 1 1 1 NA 1 1 ... $ s1cm : Factor w/ 2 levels "No","Si": 1 2 NA 1 1 1 2 NA 1 1 ... $ ovt : num NA 93.4 NA NA NA ... I declared the sampling design: > sii.design <- svydesign( id = ~1, strata = ~stratum, weights = ~expfc, data = subset(sii.tesis, !is.na(stratum))) Then I tried to get the result: > svyby(~ovt, ~d7, sii.design, svymean, na.rm = TRUE, level = 0.95) but i get the error: Error in tapply(1:NROW(x), list(factor(strata)), function(index) { : arguments must have same length The length of both variables is the same. If the variable ovt exists, there is a d7 match in the data frame. I try the same thing using another variable instead - "role" (d6) - and it works. > svyby(~ovt, ~d6, sii.design, svymean, na.rm = TRUE, level = 0.95) d6 ovt se Estudiante Estudiante 71.01805 1.370569 Profesor Profesor 72.30923 6.518378 Administrativo Administrativo 75.69102 3.715050 If I use the recategorized d7 variable (d7c, two levels only) it works too: > svyby(~ovt, ~d7c, sii.design, svymean, na.rm = TRUE, level = 0.95) d7c ovt se No estable No estable 70.92344 1.37460 Estable Estable 74.53719 4.16954 What could be the problem? Regards. Martin Canon Colombia, South America ______________________________________________ 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.