Make a Decision
Which treatment appears more successful?
Two treatments were tried. Looking only at the overall results, choose one.
Treatment A
45 of 100 successful
Treatment B
55 of 100 successful
Commit
Before seeing the success rates inside the groups, what do you predict?
The same 200 cases can be separated by how difficult they were to treat.
Treatment A
Treatment B
Which pattern do you expect inside the two groups?
Look Again
Mild cases
Severe cases
Treatment A has the higher success rate in both groups.
Yet Treatment B has the higher success rate overall.
Flip the View
Toggle the same data back and forth. No case changes. Only the grouping changes.
B treated mostly mild cases, where success was common. A treated mostly severe cases, where success was harder. The mix changes the overall comparison.
Understand
The totals hid an important difference in who received each treatment.
Treatment A
of its cases were severe
Treatment B
of its cases were mild
An overall average can reverse the pattern seen inside every group when the groups are represented in very different proportions.
Apply It
School B has a higher overall graduation rate than School A. Before deciding which school is doing better, what would be most useful to examine?
When a total seems to tell a clear story, ask: “What happens when we separate the same data into groups?”
Apply It Again
Two baseball hitters have these overall batting averages: Player A: .280 Player B: .300
Before deciding that Player B was better in every situation, what would be most useful to examine?
Before trusting an overall comparison, check whether different mixtures inside the totals could be creating the result.