I felt the survey was okay and I was happy to answer the income question - and yes, as with the age and employment status questions, it is to try to get some idea of demographics.
I think the later survey questions changed depending on your answers to previous questions (such as why or how often you used Trove), so many of us would probably have been asked different questions.
This was a lot better than one compulsory work-related survey I was required to undertake, which was clearly designed to get positive results. It only allowed "excellent/very good/satisfactory" or "greatly improved/improved/about the same" responses, with no ability to indicate that things were bad and had gotten worse, when there had been marked deterioration in many areas.
Regards, Ron
