Standard & Poor's

will add

Concord EFS


to the

S&P 500

index after the close of trading Friday to replace


(CEN) - Get Report

, which is splitting into two independent companies.

Concord EFS is currently a member of the

S&P MidCap 400

. Ceridian will become two separate companies, Ceridian and


. The new Ceridian will replace Concord EFS in the S&P MidCap 400, while Arbitron will replace

New Century Equity Holding


in the

S&P SmallCap 600

. New Century is being removed for lack of representation.


MDU Resources

(MDU) - Get Report

will replace



in the S&P MidCap 400 index after the close of trading on Tuesday. S&P 500 component


(AES) - Get Report

is acquiring Ipalco, and the companies expect to close the transaction on that day.

Elantec Semiconductor


will replace

Morrison Management Specialists

(MHI) - Get Report

, which is being acquired by

Compass Group

, in the S&P SmallCap 600 after the close of trading Friday.