Dr Aris wants to investigate the impact of a mindfulness meditation app on stress levels. He measures the physiological stress of 20 participants by recording their salivary cortisol levels (measured in micrograms per deciliter, μg/dL\mu\text{g/dL}μg/dL) immediately before a high-pressure presentation, and then again before a similar presentation after they have used the meditation app for two weeks.
Dr Aris wants to see if there is a significant difference in salivary cortisol levels between the two conditions.
Explain which statistical test Dr Aris should use to analyse his data.
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.