In the classic study by Piliavin et al. investigating bystander behavior on the New York subway, which sampling technique describes how the participants (passengers) were obtained?
opportunity
volunteer
random
stratified
105 exam-style questions on OCR A Level Psychology Responses to people in need, covering Piliavin et al. (1969): Subway Samaritan and Levine et al. (2001): Cross-cultural altruism. Each one has a worked solution and a mark scheme showing where the marks go.