Appleton blames compensation plans for some of the gender imbalance.
He said many dealers pay employees a lot but provide shoddy benefits, allowing them to opt to buy better benefits if they want to. "The typical millennial woman might look at the overall [human resources] benefits and want better," Appleton said.
Dealer Enessa Carbone, who recently sold Carbone Auto Group to Lithia Motors Inc., said women represent about 20 percent of Carbone's 640 employees, with most of them in management positions. She has worked hard to make her dealerships' culture female-friendly.
"You have to take care of the culture in the store to make a woman comfortable enough to stay and other team members to treat her well," said Carbone, now a Lithia platform vice president.
Store leaders and male employees have to understand women, and that only happens with a strong human resources department, she said.
"You need HR professionals to resolve this human resource issue," Carbone said. "One of the places where the auto industry has historically lagged is having a strong HR department in a store."
The study showed that for all staffers, dealerships' three-year employee retention rate fell to 45 percent last year, while the rate in the U.S. nonfarm private sector was 67 percent. The dealership figure has declined steadily from 51 percent in 2013, the first year of the study. That continues to hurt productivity and profits, Szakaly said.
Productivity, measured as monthly gross profit per employee, rose just 0.4 percent to $8,446 in 2015, the study said. It rose 3 percent in 2014 vs. 2013.
"Productivity for a dealership employee is really something that occurs because of on-the-job training," Szakaly said. "When you look at someone not wanting to stay for three years, let alone for a six-month training period, that's bad because just when they're doing the best they possibly can for you, they leave."