Researchers investigate how confidently customers use self-service checkouts. From a control room, two trained observers watch a live camera feed and use the same written rule: add one tally whenever an assistance light appears. The light appears when a customer requests help, but it also appears when the checkout automatically asks a member of staff to approve a restricted item. The length of the observation period is not kept the same across the different days, but the researchers compare the total tallies for each day.
Explain how the procedure could cause one reliability problem and one validity problem.
173 exam-style questions on OCR GCSE Psychology 7.3 Analysing Research, covering 7.3.1 Types of Data, 7.3.2 Measures of central tendency, 7.3.3 Other descriptive statistics, 7.3.4 Tables, Charts and Graphs, 7.3.5 Reliability, 7.3.6 Validity and effects on validity, and 7.3.7 Sources of bias. Each one has a worked solution and a mark scheme showing where the marks go.