Tax credits are exploding in popularity in Massachusetts. Over the last several years, state lawmakers have approved tax credits to lure movies and movie stars to the state, to redevelop historic buildings, and most recently to give a boost to life science companies.

The tax credits are having an impact. At least 88 movie productions filed applications for film tax credits through the end of February, according to the state Revenue Department. Numerous historic buildings that otherwise wouldn’t be redeveloped are being returned to the tax rolls. And the new $1 billion life science law is creating a lot of favorable buzz in the industry.

What’s unclear is whether these tax credits represent the best use of state dollars. Supporters usually point to the investments triggered by the tax credits, run these investments through the wash cycle of economic multipliers, and hang the resulting magnificent sum out to dry as a shining economic success story.

But what’s needed is an analysis that compares the benefits of one type of tax credit to another or to a regular state appropriation. Is a $20 million tax credit for movie productions a better use of state money than a $20 million tax credit for the restoration of historic buildings or $20 million spent improving the state’s education system?

These are not easy questions to answer, yet right now we’re not even asking them. As Ben Forman and John Schneider of MassINC write in this issue, many tax incentives lose their focus over time. Forman and Schneider say Massachusetts invests more than half a billion dollars each year in business incentives, but less than 5 percent goes to economically distressed areas.

What are our tax credit priorities? Right now, Massachusetts values movie productions a whole lot more than historic rehabilitation projects or life science companies.

Massachusetts is offering a 25 percent tax credit to movie productions that film here, with no cap on the number of credits that can be issued. So whatever the producers of the science-fiction film The Surrogates pay star Bruce Willis, they get 25 percent back from the state.

By contrast, developers trying to put abandoned or rundown historic buildings back on the tax rolls can receive up to 20 percent of qualified rehabilitation expenditures as tax credits. But they must compete against each other for the $50 million in historic rehabilitation tax credits issued each year. Toss an elephant into the room, like the Boston Red Sox rehab of Fenway Park, and suddenly there are not a lot of tax credits left over for economic redevelopment projects in struggling cities like New Bedford and Lawrence.

Despite its $100 million-a-year price tag, the new life science law contains nine tax incentives that are unlikely to stretch very far. The Revenue Department has estimated just seven of the incentives could have an annual revenue impact of more than $100 million, yet the law allows the Massachusetts Life Sciences Center to hand out only a quarter of that amount.

Should the state be putting more money into life science or historic rehabilitation tax credits? Should less be going to films? More transparency in the way tax credits are issued could help answer some of these questions.

The Revenue Department occasionally releases some aggregate numbers on how many film tax credits the state has handed out, but nowhere can you find out how much the state is paying Ashecliffe to film in town.

The historic rehabilitation tax credit program has been around nearly five years, but Secretary of State William Galvin, who administers the program, is tight-lipped about how he makes the awards and to whom he is awarding them. As our cover story reports, it took CommonWealth nearly two months to pry loose some of this information, and then only after filing a public records request.

In Maryland, anyone wanting to know who’s receiving historic rehabilitation tax credits can find it on the website of the Maryland Historical Trust. It’s right there, along with how the staff of the trust rated each project.

Perhaps the Massachusetts Legislature should require an audit of the state’s tax incentive programs periodically to see where the money is going and what the return on investment is. As author Archon Fung says in this issue’s Conversation, transparency done right can yield tremendous benefits.