Question: The stimulant Ritalin has been shown to increase attention span and improve academic performance in children with ADHD. To demonstrate the effectiveness of the drug, a researcher selects a sample of n=25 children diagnosed with ADHD and measures each child’s attention span before and after taking the drug. The data show an average increase of attention span of Md= 6.8 minutes with standard deviation of s=5.5.

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

b) Compute r ² and estimate Cohen’s d to measure the effect size of the drug.