Why am I asked so often for my master data (age, gender, etc.)?

In the surveys themselves you will usually be asked again for your age, gender, place of residence, possibly your income, etc. On the one hand this aids identification, so that we know the person filling in the survey is the same person who registered with us. On the other hand, we may only use the data you have entered in your profile to select surveys and may not pass it on to our customers.