NEW YORK (Reuters) - Activist investor Keith Meister is not embarrassed about lagging behind other corporate agitators, saying his rivals' work has led him to buy companies such as Illumina ( ILMN ), Dollar Tree ( DLTR ) and Fortrea ( FTRE ) where he argues the stocks are due for big gains.

"They have already done the work and we think they are credible," said Meister, founder of Corvex Management, referring to the work of his former boss, Carl Icahn, Paul Hilal who runs Mantle Ridge, and Jeff Smith who runs Starboard Value.

Following other activists into a stock, he said at the 13D Monitor Active-Passive Investor Summit in New York on Tuesday, can be a productive strategy.

Icahn ran a proxy fight at gene-sequencing company Illumina ( ILMN ) in 2023, won a board seat and soon after saw a new chief executive arrive.

Hilal campaigned for change at retailer Dollar Tree ( DLTR ) and brought in a new CEO from rival Dollar General where the executive had already overseen improvements.

Smith nudged contract research organization Fortrea Holdings ( FTRE ) to make changes.

Meister said these firms have done considerable research and made sensible suggestions that kick-started change. But improvements take time and he said he was able to buy into these names at opportune times.

Meister sees room for Illumina's ( ILMN ) stock price, which has already gained 24% in the last 52 weeks, to gain 50% more. Similarly, he said Dollar Tree's ( DLTR ) stock price could rise 50%, having dropped 39% in the last 52 weeks. Fortrea's ( FTRE ) stock price has dropped 36% in the last 52 weeks and Meister said he thinks the stock can surge as much as 42%.