The stimulant Ritalin has been shown to increase attention span and improve academic performance in children with ADHD (Evans et al., 2001). To demonstrate the effectiveness of the drug, a researcher selects a sample of n = 20 children diagnosed with the disorder and measures each child’s attention span before and after taking the drug. The data show an average increase of attention span of M_D = 4.8 minutes with a variance of s² = 125 for the sample of difference scores.

a. Is this result sufficient to conclude that Ritalin significantly improves attention span? Use a one-tailed test with α = .05.

b. Compute the 80% confidence interval for the mean change in attention span for the population.

c. Write the results of the t test and the confidence interval as they would appear in a scientific journal article.