Question: 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 = 25 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 = 6.8 minutes with a standard deviation of s = 5.5.

a. Is this result significant to conclude that Ritalin has a significant effect on attention span? Use a two-tailed test with α = .01.

b. Compute r² and estimate Cohen’s d to measure effect size of the drug.