WASHINGTON — The Department of Veterans Affairs has for years assigned star ratings for each of its medical centers based on the quality of care and service they provide, but the agency has repeatedly refused to make them public, saying they are meant for internal use only.

USA TODAY has obtained internal documents detailing the ratings, and they show the lowest-performing medical centers are clustered in Texas and Tennessee.

VA hospitals in Dallas, El Paso, Nashville, Memphis and Murfreesboro all received one star out of five for performance as of June 30, the most recent ratings period available.

Many of highest-rated facilities are in the Northeast — in Massachusetts and New York — and the upper Midwest, including in South Dakota and Minnesota. Those medical centers scored five out of five stars.

The VA determines the ratings for 146 of its medical centers each quarter and bases them on dozens of factors, including death and infection rates, instances of avoidable complications and wait times.

USA TODAY Network is publishing the ratings in full for the first time so that members of the public — including patients and their families — can see how their local VA medical centers stack up against others across the country.

Has the VA improved? Internal data show it's a mixed bag

Some lower-ranking medical centers have remained poor performers despite high-profile crises and years of attention and resources from Washington.

For instance, the Phoenix VA was a one-star medical center in 2014 when news broke that veterans had died awaiting care there while schedulers kept secret wait lists masking how long veterans were waiting for appointments. The revelations triggered a national scandal, hearings on Capitol Hill and the replacement of the VA secretary.

Phoenix remained a one-star facility in the most recent ratings. DID WE TRY TO GET A REACTION FROM PHOENIX?

VA Undersecretary for Health David Shulkin cautioned against using the star ratings as a “ranking tool” and said they are considered an “internal improvement tool.”

“It is essentially a system within VA to see who’s improving, who’s getting worse, so we can identify both,” Shulkin said.

The documents obtained by USA TODAY list star ratings for every facility for the fourth quarter of 2015. The VA subsequently agreed to provide a list of one- and five-star facilities for the quarter that ended June 30, the most recent ratings available, MEANING WHEN? but declined to identify those with two to four stars.

Shulkin said he was apprehensive about any ratings becoming public. “My concern is that veterans are going to see that their hospital is a 'one' in our star system, assume that’s bad quality and veterans that need care are not going to get care,” he said. “And they’re going to stay away from hospitals and that’s going to hurt people.”

But without the star ratings, members of the public — including patients, members of Congress and others outside the agency who could hold it accountable — have no way of knowing whether VA medical centers are improving or declining, except to plow through a dizzying array of hundreds of spreadsheets on the agency’s website.

“The data’s there, but you’d have to be an expert to get through it,” Shulkin conceded.

He said 120 of the 146 medical centers that the VA rates on the star scale have shown improvement since he began overseeing the Veterans Health Administration in July 2015.

He said all of the one-star facilities have shown improvement except for the VA medical center in Detroit, which has declined.

Pamela Reeves, director of the Dingell VA Center in Detroit, said that officials there are "working closely with our performance improvement teams in the development and oversight of action plans to address the opportunities identified by the … data.” In Phoenix, VA officials appointed a new director in October and are pumping millions into the effort to improve the medical center.

Shulkin said that nationwide, medical centers where performance has declined are getting extra scrutiny and help from national VA officials. If they still don’t show sufficient progress, hospital management could be replaced.

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That’s what happened in Wilmington, Del., where the VA ousted the medical center’s director in October after months of deteriorating quality. Wilmington was among several hospitals placed on a “high-risk” watch list earlier this year because of declining performance, according to the internal VA documents. Also on the list were hospitals in Tomah, Wis., and Oklahoma City, Okla.

The Tomah VA Medical Center made national headlines nearly two years ago after a veteran died there when he was prescribed a fatal cocktail of narcotics. A USA TODAY investigation published last December revealed gaping lapses in care at the Oklahoma City VA.

Rep. Jeff Miller, R-Fla., chairman of the House Veteran's Affairs Committee, said the VA should immediately release all the ratings and quality data and do so on a continuing basis. He argued that the status quo — “in which VA officials often attempt to downplay and sometimes mislead the public about serious problems until it's too late” – is unacceptable.

"The secrecy with which VA treats these quality ratings is alarming,” Miller told USA TODAY. “Veterans seeking care at VA hospitals deserve to know exactly what they are walking into. Additionally, Congress, taxpayers and other stakeholders need to have a quick and efficient means of comparing the performance of various VA medical centers in order to identify facilities in need of improvement.”

Alex Howard, senior analyst at the Sunlight Foundation, a nonpartisan transparency advocate in Washington, said there’s “no rationale that I see for withholding that from veterans, much less the general public.”

“I would think the only entity that wouldn’t want that data public would be the facilities themselves, which is not sufficient cause,” he said.

The VA also rarely releases nationwide averages showing overall improvements or declines in agency performance measures, so it can be hard to determine exactly what’s changed since the scandal in 2014, when President Obama tapped Bob McDonald, a former Procter & Gamble CEO, to take over as secretary and overhaul the agency.

The documents obtained by USA TODAY detail those averages, and when asked about them, VA officials agreed to provide updated statistics. Overall, the data show something of a mixed bag, with improvements in some areas and declines in others.

On average, veterans are dying at lower rates and contracting fewer staph and urinary tract infections from catheters in VA medical centers since 2014. Veterans are not staying as long in VA hospitals and they are being readmitted within 30 days at lower rates.

VA hasn't fixed wait-time problems, GAO finds

At the same time, veterans are experiencing higher rates of preventable complications during hospital stays, on average, than they did in 2014. Those on ventilators suffered more problems, such as catching pneumonia, and the rate of turnover for nurses has increased.

The VA has also seen increases in the percentage of veterans who have to wait longer than 30 days for appointments when they are new patients. Overall, more than 500,000 veterans were still waiting longer than 30 days to be seen as of Nov. 15. More than 125,000 of them were waiting longer than two months, and 46,000 were waiting more than six months.

Shulkin said half of the 500,000 appointments are for more minor needs such as dental, hearing, vision and diet consultations. “I can sleep at night,” he said. “The ones I worry about are the ones who can’t wait or shouldn’t be waiting, so that’s where our entire focus of our system is right now. I don’t care about you waiting for eyeglasses, I mean that’s poor customer service, I understand, but I do care if you have a lung nodule. I mean, that matters.”

Shulkin said the number of veterans waiting longer than a month for urgent care has decreased from 57,000 to 600 since he took over last year.

And he says he is working to ensure that veterans get same-day care — if they have urgent needs — at VA medical facilities across the country by the end of the year.

“If you have an urgent care problem, your wait should be zero,” he said.

Contributing: Detroit Free Press reporter Todd Spangler and Arizona Republic reporter Dennis Wagner, members of the USA TODAY Network.