The figure was momentous: 20,000 people are thought to be addicted to drugs in Baltimore City, according to Rachel Indek, spokeswoman for Behavioral Health System Baltimore, the city’s quasi-public drug-treatment overseer.

Buried in a Baltimore Sun story about a neighborhood’s protest against a new methadone clinic (“Planned drug treatment clinic in Harwood sparks conflict,” July 13), the 20,000 figure cried out for further exposition. It was one-third the number—60,000—formerly cited by treatment experts and politicians alike.

So, have Baltimore’s increased drug treatment and other medical and mental health services really decreased the city’s addicted population by two-thirds?

Maybe. But maybe not.

Indek says the 20,000 figure derives from a national survey taken in 2011, and is part of BHSB’s effort to get a better idea about the population it serves. “Our new bosses told me we have to figure out a way to know how many people have an addiction, like to heroin, and how many want treatment and can’t get it,” she says.

The National Survey on Drug Use and Health only geographically breaks down by state and region (and includes a disclaimer explaining that some of Maryland’s data from 2008 and 2009 came from “fraudulent cases”), but allows a good extrapolation for the city itself.

The old number, cited since the early 1990s, came from a number of sources, and from an article of faith within the drug treatment community, which holds that in any population, one in 10 people will have problems with addiction. With a population of 625,000, an addict population of 60,000 seemed conservative.

But the figure was debunked in 2005 by Sun reporter Alec MacGillis. He traced it to a 1986 study that extrapolated from numbers of people seeking treatment. More than a decade later the Center for Substance Abuse Research produced a report with four separate estimates of the number, MacGillis wrote, with the largest one at 60,000.

But that estimate included alcoholics. “The most reliable estimate for illicit drug addiction, the study found, was only 20,711,” MacGillis wrote.

In other words, the number of heroin and cocaine addicts in Baltimore City was only about 20,000 as of 1998 or so, if that estimate had any validity.

In 2006 Dr. Joshua Sharfstein, currently Maryland’s secretary of health and mental hygiene but then Baltimore’s health commissioner, guessed the number at 50,000. But he was clear it was just a guess.

Why is it so hard to get a fix on the number of addicts?

As a matter of science, it’s not that difficult. Psychologists have a clinical measurement they use, based on a questionnaire, to determine which patients suffer from addictive personality disorder or substance abuse. Drug treatment providers are supposed to document every patient and the state is supposed to keep records of how they progress. So the number of addicts in treatment (as well as the number who relapse) should be as simple to find as any other data query.

But until recently, figures were kept in several different “silos,” Indek explains. BSAS—its name before its merger last year with Baltimore Mental Health Systems—tracked only people who needed substance-abuse treatment and did not have any kind of health insurance. Those with private health insurance, and those with Medicaid, were tracked by other organizations. Or not at all.

All this began to change in 2010, when federal rules governing Medicaid funding and private insurance began to change under the Mental Health Parity and Addiction Equity Act. Henceforth, Health Secretary Kathleen Sebelius announced, the government would consider mental health care to be “health care.” And addiction services were on their way to becoming mental health care. Suddenly, much more money was linked to the clients or patients directly, and much less was allotted to programs and outreach.

That trend has continued with the Affordable Care Act. Today, pretty much everyone who is poor is eligible for Medicaid, and under Medicaid, both substance-abuse treatment and other mental health care are eligible to be paid for under the program.

Mental health and addiction services will be tracked the same way, potentially giving public health officials better data about the population in need.

Baltimore merged its mental health and addiction oversight organizations last year. Maryland is doing the same, Indek says. And that means that pretty soon the real number of addicts will be known—or at least knowable.

“By 2015 all the data will be going into one place so we’ll access to that data,” she says.

In the meantime, Indek is trying to learn how many people will need drug treatment and mental health services, so BHSB can size the city’s drug and mental health treatment system appropriately.

“Theoretically everyone could get coverage and get the treatment they need, but that’s not really true,” Indek says. “So we’re trying to make sure there is enough treatment available so those who do need treatment can get it.”