A Wall Street sign is seen in Lower Manhattan in New York, January 20, 2016. REUTERS/Mike Segar

FRANKFURT (Reuters) - Investors earned millions of dollars in profits from correctly betting on market moves ahead of sensitive U.S. economic data, suggesting leaks of key indicators, a European Central Bank research paper said on Monday.

Studying moves in the case of 21 market-moving indicators between 2008 and 2014, 11 showed some pre-announcement price drift consistent with the announcement surprise, with seven of them indicating substantial moves, the authors said in the paper, which does not necessarily represent the ECB’s opinion.

“Based on a back-of-the-envelope calculation, we estimate that since 2008 in the S&P E-mini futures market alone the profits associated with trading prior to the official announcement release time have amounted to about $20 million per year,” the authors said.

“Prices start to move about 30 minutes before the official release time, and this pre-announcement price move accounts on average for about a half of the total price adjustment.”

Data that showed “strong” evidence of pre-announcement price moves included the CB consumer confidence index, existing home sales, preliminary GDP, industrial production, the ISM Non-manufacturing index, the ISM Manufacturing index and pending home sales, the paper said.

“While the overall evidence points to leakage and proprietary data collection as the most likely sources of pre-announcement drift, reprocessing of public information may also contribute to some extent,” the paper said, arguing that leakage cannot be conclusively established.

“To ensure fairness in financial markets, strict release procedures need to be implemented for all market-moving announcements including announcements originating in the private sector,” the paper said.