You have been asked to select a 10 per cent sample of firms from the sampling frame used for self-check question 7.3.

a Select a 10 per cent systematic random sample and mark those fi rms selected for the sample on the sampling frame.

b Calculate the average (mean) annual output in tens of thousands of pounds over the past year for your sample.

c Given that the true average annual output is £6,608,900, why does systematic random sampling provide such a poor estimate of the annual output in this case?