Dr. Owusa is studying the impact of alcohol on disrupting cognition. He measures cognitive disruption by measuring reaction time in milliseconds (where he finds a mean score of 185), by measuring how many errors people make in trying to recall a 20 item list studied for 30 seconds (where he finds a mean of 7 errors) and by tracking how many errors people make when reciting the alphabet backwards starting at G (where he finds that on average people make 5 errors). He wants to combine these scores together to create one composite score of cognitive disruption per participant. What should he do to get good composite scores