Codebook for the categorical variables registered in the data set files (see csv files).

the variable `sex` codes as follows:
0 -> man
1 -> women

the variable `age group` reads as follows:
20 -> 20-29 yrs-old
30 -> 30-39 yrs-old
40 -> 40-49 yrs-old
50 -> 50-59 yrs-old
60 -> 60 yrs-ol and over