I don't get it, do you have something to hide or are you just being a shit disturber????
It's a simple f@#*king questionnaire that takes less than 5 minutes and it's over. Do you really care if they want your day of birth?? I don't, so I just give it to them and they're off my back. The government uses the stats for various planning activities to better serve society in the future, that's why we have a great country, we plan for things unlike other countries, we don't react when it's too late.
They ask for your name and contact number in the event they have to contact you if they are unable to decipher some of your answers and in 99% of the time it's never used, the other data is compiled into a database in general categories with no personal name attached, it's group stats, nothing personal included. If you make a call to their toll free line you'll get all your answers.