Used-vehicle valuation and residual value forecast provider Black Book reported its Used Vehicle Retention Index fell to 113.6 in April, a 0.2% decline from March. Despite the index now falling for five straight months, it is still 1.4% higher than the 112 registered a year ago.

A total of 14 segments finished the month in positive change territory, led by premium sporty cars (up 1.4%), full-size vans (1.2%), and compact crossovers (1.1%).

The index has dropped each month since November, reflecting a late start to the spring selling season, analysts said. SUVs and luxury vehicles showed the largest declines in March. Market share changes reflect a continued shift away from cars and toward more SUVs and light trucks.

"That the index has declined for five straight months and it is still slightly higher than where it was a year ago is a testament to the sheer strength in the market we saw throughout 2018," said Anil Goyal, Black Book's executive vice president of operations. "Much of the 2018 activity was spurred by economic strength, resulting in significant demand for affordable used sedan values. It will be difficult to replicate that activity over the remainder of 2019."

The Black Book Used Vehicle Retention Index is calculated using Black Book's published Wholesale Average value on two- to six-year-old used vehicles, as percent of original typically equipped MSRP. It is weighted based on registration volume and adjusted for seasonality, vehicle age, mileage, and condition.