search for: sav3

...;- lme(yi ~ xi, random = ~ 1 | id, data=dat) sav1 <- augPred(res1, primary = ~ xi) # WORKS dat$zi <- "a" res2 <- lme(yi ~ xi, random = ~ 1 | id, data=dat) sav2 <- augPred(res2, primary = ~ xi) # WORKS dat$zi[10] <- NA res3 <- lme(yi ~ xi, random = ~ 1 | id, data=dat) sav3 <- augPred(res3, primary = ~ xi) # ERROR The error message: Error in `[[<-.data.frame`(`*tmp*`, nm, value = c(1L, 1L, 1L, 2L, 3L, : replacement has 10 rows, data has 4 So, if 'zi' is a factor, then a missing value causes no problems (sav1). Or if 'zi' is a character var...