A factory manager is concerned with employee turnover. In a typical year around 85% of the employees who were working at the beginning of the year are still working in the factory at the end of the year. Last year the rate was only 65%. The manager implements a more flexible schedule for the employees in an effort to make them happy. At the end of that year the retention rate for the factory workers is 79%, and the manager gets a pay raise for "solving the problem".

1. Below is a list of threats to validity. Identify which of them is most likely to provide an alternative explanation for the results.

Attrition

History

Maturation

Regression

Retesting

Selection

2. Explain how this threat to validity could explain the results.