Julian conducted a study investigating the impact of a 10-minute daily meditation app on stress levels in a small sample of 15 university students. He recruited participants using volunteer sampling via a post on a social media group, and measured stress levels using a self-report questionnaire. Explain one improvement Julian could make to his study.
638 exam-style questions on Edexcel A Level Psychology Methods. Each one has a worked solution and a mark scheme showing where the marks go.