U.S. employees are far more likely to go out of network and see lower reimbursement for behavioral health services than for physical health services. Despite a nationwide push for parity, those equality gaps are widening, according to a new study.

The report — published by Seattle-based actuarial and consulting firm Milliman Inc. and commissioned by the Mental Health Treatment and Research Institute LLC, a not-for-profit subsidiary of The Bowman Family Foundation — dove into the data of 37 million workers and their dependents with commercial preferred provider organization (PPO) plans from 2013 to 2017.

Researchers found that disparities between behavioral health services and physical health services during that time actually increased.

For example, in 2013, inpatient behavioral health facilities were 2.8 times more likely to be out of network than medical or surgical inpatient facilities. By 2017, that likelihood grew 85%, with behavioral health facilities 5.2 times more likely to be out-of-network.

When it came to outpatient facilities, researchers found a similar correlation. Behavioral health providers were 5.7 times more likely to be out-of-network than their medical counterparts in 2017 — up 90% from five years earlier.

The list of behavioral health discrepancies goes on and continues into the realm of reimbursement, though to a slightly lesser degree, according to the study.

Across the board, the average reimbursement for behavioral health providers between 2013 and 2017 was lower than for medical providers, and that gap also worsened slightly over time.

Take office visits, for example. In-network reimbursements for primary care visits were nearly 24% higher than for behavioral health visits in 2017, up three percentage points from 2015.

And in 2017, 11 states saw reimbursement rates for primary care visits that were more than 50% higher than for behavioral health visits. That number from from nine states in 2015.

Given the findings, Milliman researchers advised health plan to carefully review their processes to ensure compliance with the federal Mental Health Parity and Addiction Equity Act (MHPAEA), which generally requires insurers to cover mental health and substance use disorder (SUD) treatment the same as they would for treatment of other diseases.

“While MHPAEA federal rules state that disparate results are not in and of themselves definitive evidence of noncompliance, significant disparities, such as high out-of-network use of behavioral health providers and/or lower reimbursement for behavioral providers, could point to compliance problems,” they wrote.

However, the researchers declined to provide an opinion on discrepancies within reimbursement rates, noting that they’re “impacted by many processes and factors.”