The first quarter marked the first year-over-year decline in NADA Used Car Guide’s measure of used-vehicle prices in about seven years.

And if this keeps up, used values will fall on an annual basis for the first time since 2008.

NADA Used Car Guide said in a news release accompanying its monthly Guidelines report that its seasonally adjusted used-vehicle index for March was down about 1 percent from February.

The reading of 118.6 represents a five-year low.

Used prices were actually up 1 percent in March, but over the prior seven years, they had increased an average of 2.7 percent in March, NADA Used Car Guide explained.

Hence, the index going lower.

“We saw the index down as we closed out the first quarter of the year as well,” NADA Used Car Guide executive analyst Jonathan Banks said in the news release.

“Compared to Q1 of 2015, it was down 3.6 percent,” he said. “It was the first year-over-year decline we've seen since 2009.”

In the Guidelines report, analysts forecast a 1.3-percent to 1.8-pecent sequential decline in April for prices of used cars up to 8 years old. The past two years, they note, the decline has averaged 1.1 percent.

May is likely to show a 3-percent decline, with June and July showing some stabilization.

But here’s the kicker: full-year used-car prices are likely to drop between 5 percent and 6 percent year-over-year on an index basis, NADA Used Car Guide said.

The last “material decline” in used prices?

2008.