The following error was brought to my attention by Rose Cummins (thank you):

Page 124 The text for the field experiment should be ‘A psychologist carries out a field experiment into helping behaviour. He uses opportunity sampling. On one day he arranges for a young man in a hooded top and jeans to collapse in a local shopping centre. On the next day he arranges for a young man in a suit to collapse in the same shopping centre. He notes the number of people who stop to help each day, and these are shown in the bar chart below.’