hello;
I am a Ph.D student in ELT department and investigate avoidance of English phrasal verbs by Turkish and Dutch learners to see the effects of similarities and difficulties between native language and target language on avoidance behaviour.
I also have to collect data from native English speakers to compare results with the ones obtained from Turkish and Dutch learners.
I hope native speakers contribute to my research by completing my online survey. It takes not more than ten minutes.
thanks in advance for your time and participation.
http://goo.gl/cXpsNP
http://www.surveycrest.com/survey/5363fdc75813e

For question 4, it suggests 'lets down his friends', but I think the option should be 'lets his friends down'?

It's also a bit biased for me filling out this test, because once I started ticking off a few of the phrasal verbs, I started always going towards them to complete the sentence.  You might want to make the test with a few control questions where there are some questions that don't include phrasal verbs as answers, so that the test takers don't catch on that you're asking them how many situations they'd use them in.

I have checked 'let down' and 'let sb down' at Corpus of Contemporary English. The frequency of use of 'let down' is more predominant than the other; however, both of them is possible and I should add that I am not assertive on this issue. You know better than me. I am a foreign language learner 
I will keep in mind your admonition related to adding extra questions not consisting of verb-particle construction as an option.
By the way, thanks for completing and submitting the whole survey.
I will be glad if you share it with people around you. Participation is really very low.
Thank you...