[nikkev]

To add to your second point, Andrew Gelman had some blog posts earlier this year detailing the challenges of doing online surveys, where he used simple questions that respondents "should" have been able to answer in a survey and found that a fair percentage >10% answered some of these simple questions wrong. I am assuming there is no incentive for answering more questions correctly so it's possible that some respondents may have answered blindly to finish quickly leading to lower scores.