Before the professional intelligence measurement question, please add something like:

Please ESTIMATE your IQ, using a standard average of 100 and stdev of 15.

It might make sense to add on something like:

You may want to check a normal distribution calculator (such as http://stattrek.com/online-calculator/normal.aspx ) to ensure you aren't overestimating.

Or, alternatively, we could get at the same sort of question by asking this:

Please estimate how many people would have to be in a group of adults, chosen uniformly at random, for you to expect the group to contain one (and only one) person smarter than you.

But it's not obvious to me that this is a thing people would be good at estimating.