A psychologist investigates whether displaying a countdown timer affects visual-search accuracy. Each participant completes two matched symbol-search sheets, each containing 30 target symbols. Participants have three minutes to circle as many target symbols as possible on each sheet. Straight after finishing one sheet, each participant completes the other.
| Countdown timer | Order completed | Mean number of target symbols correctly circled out of 30 |
|---|---|---|
| Not displayed | First | 17.4 |
| Displayed | Second | 21.6 |
The psychologist concludes that displaying the countdown timer improved visual-search accuracy.
Explain why the psychologist cannot be certain that this conclusion is valid. Use the results in your answer.
182 exam-style questions on OCR GCSE Psychology 7.1 Planning Research, covering 7.1.1 Hypotheses, 7.1.2 Variables, 7.1.3 Experimental Designs, 7.1.4 Populations and Sampling, 7.1.5 Ethical issues, and 7.1.6 Dealing with ethical issues and BPS Code. Each one has a worked solution and a mark scheme showing where the marks go.