A university provides two different drop in maths help centres, staffed by different tutors. They have randomly sampled 30 users of each centre and done a quick user satisfaction survey. The results are shown in the table below

	Satisfied users	Unsatisfied users
Drop-in help centre A	18	12
>Drop-in help centre B	11	19

a) [2 marks]Is this an example of an observational study or an experiment? Explain how you can tell?

b) [2 marks]Which variable is explanatory and which is the response?

c) [3 marks]What is the relative risk of a someone being unsatisfied after visiting centre B compared to centre A? Interpret what this means.

d)[2 marks] What test could you use to determine if there is an association between centre and satisfaction? What should your null hypothesis be?

e) [1 mark] Assuming the null hypothesis is true, how many unsatisfied users would you expect to see that visited centre B?

f) [2 marks] If you get a very small p-value for the test suggested in part d, would it be appropriate to conclude that the staff at centre A are more competent than the staff at centre B? Explain your answer.

g) [2 marks] Some people have proposed that the different locations and opening hours of the two centres might be confounding variables. Explain what is meant by a confounding variable.

h) [2 marks] Explain what key feature of an experimental design helps you to control for confounding variables. Would it be possible to do such an experiment in this scenario?