Introduction to Stata 8 - (GRIPS

Or you can extract key information from a CPR number read as one string variable (cprstr):
generate bday = real(substr(cprstr,1,2))
gen bmon = real(substr(cprstr,3,2))
gen byear = real(substr(cprstr,5,2))
gen control = real(substr(cprstr,7,4))
gen pos7 = real(substr(cprstr,7,1)) // to find century
Before creating bdate you must decide the century of birth; see the rules below:
generate century = 19
replace century = 20 if pos7 >= 4 & byear = 5 & pos7 = 58
replace byear = 100*century + byear
generate bdate = mdy(bmon,bday,byear)
The information on sex can be extracted from control; the mod function calculates the
remainder after division by 2 (male=1, female=0):
generate sex = mod(control,2)
Century information in Danish CPR numbers
The 7th digit (the first control digit) informs on the century of birth:
Pos. 5-6 (year of birth)
Pos. 7 00-36 37-57 58-99
0-3 19xx 19xx 19xx
4, 9 20xx 19xx 19xx
5-8 20xx not used 18xx
Source: www.cpr.dk
Validation of Danish CPR numbers
To do the modulus 11 test for Danish CPR numbers first multiply the digits by 4, 3, 2, 7, 6, 5,
4, 3, 2, 1; next sum these products; finally check whether the sum can be divided by 11.
Assume that the CPR numbers were split into 10 one-digit numbers c1-c10. Explanation of
for : see section 7.
generate test=0
for C in varlist c1-c10 \ X in numlist 4/2 7/1 : ///
replace test=test+C*X
replace test=mod(test,11) // Remainder after division by 11
list id cpr test if test !=0
To extract c1-c10 from the string cprstr:
for C in newlist c1-c10 \ X in numlist 1/10 : ///
gen C=real(substr(cprstr,X,1))
To extract c1-c10 already when reading data:
infix str10 cprstr 1-10 c1-c10 1-10 using c:\...\dfile.txt
I developed an ado-file (cprcheck.ado) that extracts birth date and sex information and checks
the validity of a CPR number. Find and download it by:
findit cprcheck
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