Dear Ekaterina, I enclose a copy of the Baker McKenzie report titled, GDPR National Legislation Survey issued in January 2018 and it covers a number of your queries.

Dear Ekaterina, that is a good question and I think it cannot be answered yet. I am working for GESIS and we conduct e.g. the German General Social Survey ALLBUS. Currently all survey consent forms are being updated, and I would expect that if social reserach follows the demands of data protection officers to fully spell out the ways and workings of data processing than this would have a negative impact in the repsonse rates. Wording and extend of a consent form might have an impact on response rate as Elinor Singer, Norbert Schwarz and others have pointed out.

A dated overview on the literature concerning consent procedings and repsonse rates can be found in Singer (1993):

http://www.jos.nu/Articles/abstract.asp?article=92361

Thers is a lot of specialized research on the topic,

e.g. on broad consent in biobanks:

Article Public Attitudes toward Consent and Data Sharing in Biobank ...

or on consent for linking survey and panel data with adminstrative records:

https://academic.oup.com/poq/article/81/1/131/2666516

or

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679.9460&rep=rep1&type=pdf

Informed consent is the the silver bullet of academic social reserach using surveys but as reserach shows consent forms need to strike a balance between "sufficient" information and legal information overload. And GDPR recital 39 reads:

" The principle of transparency requires that any information and communication relating to the processing of those personal data be easily accessible and easy to understand, and that clear and plain language be used."

Best,

Oliver.

Thank you very much for your responses, dear Oliver, and dear Samy! I hope the information you shared will be of use for other researchers.