A study issued Wednesday says an expansion of casino gambling in Maryland will not produce the kind of revenue supporters say it will, the Baltimore Business Journal reported.

About 45 percent of the revenue promised from adding a casino in Prince George’s County and table games at Maryland casinos is existing gaming revenue, according to the study issued by the Maryland Public Policy Institute, a nonpartisan think tank based in Rockville.

Supporters of Question 7, the gambling expansion referendum, on the other hand, have said an expansion would generate $199 million annually for Maryland schools.