This blog post describes how South African ID numbers can be verified mathematically in Survey123. South African ID numbers have the following format:
{YYMMDD}{G}{SSS}{C}{A}{Z}
YYMMDD : Date of birth.
G : Gender. 0-4 Female; 5-9 Male.
SSS : Sequence No. for DOB/G combination.
C : Citizenship. 0 SA; 1 Other.
A : Usually 8, or 9
Z : Control digit
The most challenging part of verifying the ID number is the control digit which is calculated by using the Luhn algorithm – this will be the focus of this blog post.
The best way to tackle complex mathematical functions in Survey123 is to break it up into separate mathematical calculations and using calculated fields:
The check digit is the last digit of the SA ID number so it can be retrieved with the following function: substr(${idnr}, string-length(${idnr}) – 1, string-length(${idnr})) where ${idnr} refers to the captured ID number.
Once you have an understanding of the substr() function the rest of the calculations used to verify the ID number is pretty much straight forward.
The survey’s XLSForm file can be found here (and can be freely used): SA Id number
- Copy the file to your downloads folder
- Open Survey123 Connect
- Create a New Survey and base it on an existing file
- Choose the Excel file that you have downloaded
- Your survey will be generated
Notes:
- The SA ID Number does not indicate if a user was born in 19yy or 20yy so both options are catered for – with a logic test to see if the birth date is in the future (age not greater than zero)
- Race is no longer indicated in the SA ID Number