Calculating the cost of tax breaks in Mass.

Massachusetts over the past 16 years has more than doubled the amount of tax breaks it provides businesses to spur economic development but has only a vague idea whether the incentives are worthwhile, according to a new study by a Boston think tank.

The Massachusetts Budget and Policy Center found that the cost of the 58 “special business tax breaks” — covering everything from making movies to selling aircraft parts — has jumped to $770 million from $342 million in 1996. Unlike traditional spending items, such as grants or highway projects, tax breaks are generally not included in the state’s annual budget, so they don’t receive the same scrutiny as other programs.