According to a 1997 virginia pilot article, david merrell, a sixteen-year-old from suffolk, virginia, won state science-fair honors for his project in which he studied how different types of music affect the performance of mice. the subjects in merrell's project were 72 white mice, and to ensure scientific validity, each white mouse weighed between 15 and 20 grams, was 4 to 6 weeks old, and was bred to ensure no genetic abnormalities existed. during the first week of the project merrell put each mouse through a maze 3 times and established a baseline average time of about 10 minutes to complete the maze. he then randomly divided them into three music groups of 24 mice: the hard-rock group, the mozart group, and a control group. for the next 3 weeks he piped in music 10 hours/day to the hard-rock and mozart groups. the control group heard no music. he recorded the effect of the music on the completion times for the maze. merrell found that the 24 mice in the control-group managed to cut (on average) about 5 minutes from their maze-completion time, the mice in the mozart-listening group cut their time back (on average) 8-and-a-half minutes, but the mice in the hard-rock group added (on average) 20 minutes to their time. based on merrell's study, can we have confidence that type of music has a causal effect on the length of time it takes a mouse to complete a maze?