data(infert)
| 1. | Education | 0 = 0-5 years |
| 1 = 6-11 years | ||
| 2 = 12+ years | ||
| 2. | age | age in years of case |
| 3. | parity | count |
| 4. | number of prior | 0 = 0 |
| induced abortions 1 = 1 | ||
| 2 = 2 or more | ||
| 5. | case status | 1 = case |
| 0 = control | ||
| 6. | number of prior | 0 = 0 |
| spontaneous abortions 1 = 1 | ||
| 2 = 2 or more | ||
| 7. | matched set number | 1-83 |
| 8. | stratum number | 1-63 |