In the 10th year, they built 30. This variance in production rates does not show up in military production. However, by looking at commercial data, Benkard was able to prove a hunch-that learning rates vary a great deal because of the forgetting phenomenon. He found that the forgetting rate was high in commercial aircraft construction. From one year to the next, the firm retains only 60 percent of its experience.
Turnover plays a key role.
Often lower production rates are accompanied by inactivity and layoffs. There are also different kinds of turnover. If workers change jobs within the company, they have to be retrained, as do the workers who take over their old jobs. It's wise to promote people but keep them on the same team so their experience is not lost. Benkard also examined how much learning spills over from one product to another.