The basis of the survey was just under 1,000 telephone interviews conducted with persons 15 years and over who had had at least one interview for a job or a training place in the previous five years. The survey was conducted from 15 November to 8 December 2017 by the Kantar EMNID polling institute.
Knowledge about the inadmissibility of questions on protected characteristics
The report can be found here (only available in German)
A factsheet of the results in English can be found here.