Interval level of measurement.
Work Step by Step
The differences between years of birth have meaning; if the year of birth of a person is 1970 and the year of birth of another person is 1980, it means that the first person is 10 years older than the second one. The world has begun billions of years ago, so the year 1 is not the beginning. Also, the year 2000 is not the double of the year 1000.