Criminal justice data in this country is hard to come by. It can be messy and difficult to understand. And in many cases, the data doesn’t exist at all.

How many people are in jail? For what crimes? For how long? Are people in jail mostly awaiting trial? Are they there for being unable to pay bail of $500 or less? You might think we know the answers to these basic questions, but we don’t.

Missing data is at the core of a national crisis. The United States leads the industrialized world in incarceration. With nearly 5 percent of the planet’s population and almost a quarter of its prison population, the country has invested a tremendous amount of money in the corrections system without the statistics necessary to tell us whether that money is actually reducing crime, improving fairness or lessening recidivism. State and federal spending on corrections has grown more than 300 percent over the past 20 years — becoming one of the fastest-growing line items in state budgets.

No credible business would ever make this kind of investment without being able to gauge its success. Moreover, we’ve all come to expect transparency when it comes to how the important institutions in our lives — our schools and hospitals, for example — are performing. Data-driven decision-making is the norm there, as it should be for criminal justice.