library(dplyr)
mental <- data.frame(
    impair = c(17, 19, 20, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25, 26, 26,
               26, 26, 27, 27, 27, 27, 28, 28, 28, 28, 28, 29, 30, 30, 31,
               31, 31, 31, 32, 33, 34, 34, 34, 41, 41),
    lifeevt = c(46, 39, 27, 3, 10, 44, 37, 35, 78, 32, 33, 18, 81, 22, 50, 48,
                45, 21, 55, 45, 60, 97, 37, 30, 13, 40, 5, 59, 44, 35, 95, 63,
                42, 38, 45, 70, 57, 40, 49, 89),
    SES = c(84, 97, 24, 85, 15, 55, 78, 91, 60, 74, 67, 39, 87, 95, 40, 52,
            61, 45, 88, 56, 70, 89, 50, 90, 56, 56, 40, 72, 53, 38, 29, 53,
            7, 32, 55, 58, 16, 29, 3, 75))