MADISON, Wis. (AP) — About 200,000 retired public employees in the Wisconsin Retirement System will receive a 2 percent pension payment increase starting in May.

The Department of Employee Trust Funds announced the payment increase on Tuesday. It comes after the State of Wisconsin Investment Board reported that investments in the "Core Fund" rose by 8.5 percent last year and "Variable Fund" investments rose by 10.6 percent.

All public employees are covered by the "Core Fund," which levels out gains and losses over a five-year period to avoid large spikes.

The nearly 40,000 retirees who invest in the voluntary and more volatile "Variable Fund" will see a 4 percent increase. That fund is comprised of all stocks, making pension payments tied to it more subject to ups and downs.