This is a wide-ranging inquiry based in Germany which is very well documented. Usefully, those involved have been reflective about what did and didn’t work in their research.
As well as a very long and detailed questionnaire/survey tool which was too complex to be much use in practice, they also developed some shorter, more focussed inquiry tools. They also published a bulletin which included reports from call centre workers in other countries.
Resources
Kolinko – Questionnaire 1: Facts and Overview66.6KB
Kolinko – Questionnaire 2: Discussion and Agitation35.6KB
Kolinko – Questionnaire 3: Struggles58.7KB