The stimulant Ritalin has been shown to increase attention span and improve academic performance in children with ADHD (Evans, Pelham, Smith, 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 MD = 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.