NEW YORK (Bloomberg) ? Bermuda-based insurer Catlin Group Plc will join the UK's FTSE 250 Index

Joining an index can boost a company's share price because funds that track the benchmark need to buy the shares of its members. An estimated ?2 billion ($3.7 billion) in shares track the FTSE 250, according to Citigroup Inc.

"It's not bad news to get in," said Alan Beaney of Principal Investment Management in Sevenoaks, England, which manages the equivalent of $1.1 billion of assets. "If you get in, your share price has clearly been quite strong beforehand."

Alvis Plc and Burren Energy Plc will also be among companies joining the FTSE 250 Index, after their shares surged more than 80 percent this year. The software company Autonomy Corp. will leave.

CSR Plc will also join, as will GKN Plc, a maker of car and aerospace parts, that yesterday was dropped from the benchmark FTSE 100 Index.

The changes will take place as of the close of trading on June 18, according to an e-mailed statement from FTSE Group, which compiles the indexes and is owned by London Stock Exchange Plc and Pearson Plc's Financial Times newspaper.

Alvis, the maker of the Challenger II battle tank, has surged 84 percent this year. Last week, it received a takeover bid from BAE Systems Plc, Europe's biggest weapons contractor.

Burren, an oil and gas explorer operating in central Asia and western Africa, has more than doubled.

CSR, a maker of chips used in mobile phones, has jumped 46 percent since first selling shares to the public in February.

Catlin, a Bermuda-based specialty insurer and reinsurer whose shares first traded in April, has added 3.7 percent from April 1, its first day of trading.

"It's a milestone for us," Paul Goodridge, CSR's chief financial officer, said in an interview.

"It will mean a higher profile for CSR and allow us to reach more investors and researchers."

FTSE Group yesterday said Capita Group Plc, the UK's biggest supplier of administrative services, will join the FTSE 100, replacing GKN.

Autonomy, a maker of software that helps companies keep track of computer data, will leave the index.

The shares have fallen 6.4 percent in 2004.

"Moving in and out of indexes hasn't affected us in the past," said Edward Bridges, a spokesman for Financial Dynamics, the company that is responsible for Autonomy's public relations.

"It hasn't made a difference to our shareholders and it hasn't affected us commercially."

Martin Greenslade, finance director of Alvis, wasn't available for comment.

No one at Burren returned a call asking for comment.

James Burcke, a spokesman for Catlin, didn't immediately return a message left on his cell phone.

FTSE Group made the changes based on companies' market values at the close of trading yesterday.

The FTSE 250 comprises the 250 companies with the largest market values outside the FTSE 100. The FTSE 100 has the 100 biggest companies.

Together, the two make up the FTSE 350 Index.