The following work sampling data was collected from observing a retail assistant:
Activity Number of observations
Attending to customers 60
Telephone enquiries 150
Walking around 40
Reading data 30
Talking to manager 40
Talking to other workers 20
Lunch/coffee/comfort breaks 50
Dealing with customer complaints 110
The figures mean that, say, over the course of a day, it is estimated that 22 per cent of the time was devoted to dealing with customer complaints.
(a) Determine the limits of accuracy of the above calculation
(b) If the accuracy needed was to be ±1 per cent, determine the appropriate sample size.
(c) How would an operations manager use the data obtained from the exercise described?
Answer: (a) N = 4P (100 - P) /L2
N = 500
P = 22 per cent
L = SQRT (4 × 22 (100 - 22))/500) = 3.7 per cent
Therefore, P = 22 per cent ±3.7 per cent (ie we are 95 per cent confident that the true value lies between 18.3 per cent and 25.7 per cent)
(b) 88(78)/1 = 6864. Unlikely to be economically worthwhile - a sample size of 1716 would give ±2 per cent accuracy
(c) For setting targets of improvement, determining areas of improvement, cost savings, staff training.