A group (A) of 6000 people have participated in a program for prevention of a disease. Another group (B) of 5000 people did not participate in this program and serve as a control group. During the course of a year there were 36 cases of the disease in group A and 35 in group B. The result is shown in the table below according to two age categories.
| Group A | Group B | |||
| # Person years | # Cases | # Person years | # Cases | |
| Younger | 2 000 | 4 | 4 000 | 20 |
| Older | 2 000 | 4 000 | 1 000 | 15 |
| Total | 6 000 | 36 | 5 000 | 35 |
What is the appropriate method of making a comparison between the disease incidence rate between these two groups?