Duff & Phelps Corp. is being purchased by a consortium that includes affiliates and funds managed by The Carlyle Group, Stone Point Capital LLC, Pictet & Cie and Edmond de Rothschild Group. The deal is valued at $665.5 million or $15.55 per share in cash.

The offer is 19.2 percent higher than the closing price of Duff & Phelps’ shares on Dec. 28, 2012, and 27.3 percent higher than the company’s volume-weighted average share price during the 30 days ended Dec. 28, 2012. The transaction is expected to close in the first half of 2013, subject to stockholder and regulatory approvals.

Noah Gottdiener, chief executive officer of Duff & Phelps, said the deal is in the best interest of Duff and Phelps’ shareholders, “who will receive an immediate and certain cash premium for their shares. Importantly, the transaction will be structured to preserve the firm’s independence as we serve our clients in the future.”