Statistical eror predicting a due date

Question

The test results gave a date that was a month before the baby was born. The hospital sent a doctor to mrs. Stewart to try to determine why the predicted due date was so far off. Mrs. Stewart found out that the test results were based on the average birth weight of babies at that time, which was 7 pounds 1 ounce. Mrs. Stewart's baby weighed 8 pounds 12 ounces at birth. What statistical error did the testing people make that chased their result to be so far off?

Answer 1

It seems that they were extrapolating the due date using a linear model. Extrapolation errors result from extending a model outside its valid sampling range.