Research suggests that the antioxidants in foods such as blueberries can reduce and even reverse age-related declines in cognitive functioning (Joseph et al., 1999). To test this phenomenon, a researcher selects a sample of n = 25 adults aged 70 to 75 and administers a cognitive function test to each participant. The participants then drink a blueberry supplement every day for 4 months before they are tested again. The researcher compares the scores before treatment with the scores after treatment to see if there is any change in cognitive function.