Strange Data Collection Method

I was taken aback by what I found in my post box today – a letter asking me to complete a survey about my respiratory health. The Medical Research Institute tells me that (link to scan of letter (PDF)):

You have been randomly selected from the electoral roll to participate in the first phase which involves completing the questionnaire on the other side of this letter.

Personally I thought that it was illegal to use the Electoral Roll for any purpose other than elections, but it seems that there is an exception for approved scientific/health researchers.

I’d be surprised if the response rate was very high or very representative.

And no, I didn’t fill it out. Feel free to use the code and URL on the letter to go and answer it for me.