The data file earnings.dat contains 500 observations, collected from 100 individuals that have been observed over 5 time periods.
| Column | Type | Description |
| 1 | index | individual |
| 2 | index | time period |
| 3 | metric | monthly earnings |
| 4 | metric | working experience in years |
| 5 | metric | years of schooling |
| 6 | binary | 1 if male, 2 if female |
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