Standard & Poor's

will add

Concord EFS

(CEFT)

to the

S&P 500

index after the close of trading Friday to replace

Ceridian

(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

Arbitron

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

New Century Equity Holding

(NCEH)

in the

S&P SmallCap 600

. New Century is being removed for lack of representation.

Additionally,

MDU Resources

(MDU) - Get Report

will replace

Ipalco

(IPL)

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

AES

(AES) - Get Report

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

Elantec Semiconductor

(ELNT)

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.