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 mr = 4.8 minutes with a variance of52 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. compute the 80% confidence interval for the mean change in attention span for the population.