We used a quasiexperimental research design to measure the effect of state parity laws on the use of mental health care in the past year.
We pooled cross-sectional data from the 2001, 2002, and 2003 National Surveys on Drug Use and Health. Our sample included 83,531 adults 18 years of age or over with private health insurance stratified by the level of mental and emotional distress experienced in the worst month of the past year. We used a state and year-fixed effects approach to measure the effect of parity. Similar to a difference-in-difference analysis, the effect of parity was measured by comparing pre-/postchanges in mental health service use within states that switched active parity status to changes in service use within states that did not change parity status in the same calendar year. For each subgroup, we report predictions of the percentage point change in any mental health care use, prescription drug use, and outpatient care use resulting from parity laws.
Depending on the time window used to define active parity status, we found that parity increased the probability of using any mental health care in the past year by as much as 1.2 percentage points (P < 0.01) for the lower distress group and by as much as 1.8 percentage points (P < 0.05) in the middle distress group. We found no statistically significant changes in service use for the upper distress group. Whether measured differences were attributable to changes in the use of prescription drug or outpatient care also depended on the definition of active parity status.
Overall, the results of this study suggest that state parity laws succeeded in expanding access to mental health care for those with relatively mild mental health problems.