Asian Americans typically rank as healthier than the general U.S. population. But a new study says that's true only when data are looked at collectively.

Asian American subgroups have at least one health disparity that's masked by data aggregation, according to a report published Thursday from researchers at Brown University and UCLA.

Much work has been done to debunk the idea of Asian Americans as a "model minority" across multiple areas like educational attainment, employment and income — but health is a new arena, researchers say.

"When we think of model minority, a lot of the academic research focuses on identity politics and the difference between social classes," said Jennifer Nazareno, the second author of the study, which was published in the American Journal of Public Health. "But in terms of health disparities and health inequities, that is severely underresearched."

For the study, "Health Conditions, Outcomes, and Service Access Among Filipino, Vietnamese, Chinese, Japanese, and Korean Adults in California, 2011–2017," researchers analyzed data from the California Health Interview Survey, a web and telephone survey that provides data on the state's health and health care needs. They specifically looked at data from about 13,000 Asians from 2011 to 2017, said Alexander Adia, the first author of the study. The data were divided into five subgroups — Filipino, Vietnamese, Chinese, Japanese and Korean — that had enough respondents for the survey to establish unique analytic categories, the authors wrote.

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As an aggregate group, Asians in America appeared healthier than non-Hispanic whites, according to the study. But when researchers disaggregated the data, they uncovered a number of disparities, among them that Vietnamese respondents reported fair or poor health more than twice as often as non-Hispanic whites and Asians overall. Japanese respondents had a higher proportion of people who were obese or overweight than non-Hispanic whites and Asians overall, and Japanese and Koreans reported higher rates of diabetes than non-Hispanic whites and Asians overall.

The authors found that Filipinos appeared to be in the worst health of all Asian subgroups in the study. The group was found to have a greater prevalence of high blood pressure, asthma, heart disease and delayed medication usage compared to Asians overall. Filipinos also had higher levels in the first three health outcomes compared to non-Hispanic whites.

"In the broader narrative, data disaggregation for Asian Americans, especially as it pertains to health, has been seen as nice to have rather than as essential," Adia said. "What we're just trying to call out here is that the more we choose to treat data aggregation as the standard and then disaggregation as a novelty and nice to have, the more we choose to be blind to the health issues faced by the community."

Relying on aggregate health data about Asians, the authors said, could have prompted action to address disparities like obesity and diabetes, for which the group sees higher rates compared to non-Hispanic whites. But it would not necessarily encourage further investigation into the fair or poor health that more than one-third of Vietnamese respondents reported, according to the researchers, because Asians overall report an only slightly higher prevalence of it compared to non-Hispanic whites.

"Therefore, the aggregation of subgroup data into a single Asian category should be reframed as a choice that leads to inaccurate conclusions about health," the authors wrote. "Doing so ensures that efforts to protect Asian Americans' right to health are properly informed and targeted."

Researchers added that aggregate data limit the identification of future priorities for research, policy and health programs.

Robert Fullilove, a sociomedical sciences professor at the Columbia University Medical Center who was not involved in the study, said he found the research useful because it underscores the difference in findings in aggregated vs. disaggregated data.

"It's a perfect lesson plan to show folks that here are the dangers that occur if you lump a group together and fail to take account of some of the very important differences that make up that group," he said.

Authors noted that the study did come with limitations, among them that the findings are based on Asian Americans in California and may not necessarily represent Asian populations outside the state.