Gnap (1995) conducted a survey on teacher workload which was used in Exercise 15 of Chapter 5.

a. The original survey was intended as a one-stage cluster sample. What was the overall response rate?

b. Would you expect non response bias in this study? If so, in which direction would you expect the bias to be? Which teachers do you think would be less likely to respond to the survey?

c. Gnap also collected data on a random sub sample of the non respondents in the “large” stratum, in file teachnr.dat. How do the respondents and non respondents differ? Discuss briefly.