America is becoming more multiracial , but its data systems are still thinking in black and white. Why it matters: Outdated measurement systems are shaping how elections are analyzed, health risks are tracked and civil rights laws are enforced. The multiracial ("Two or More Races") population grew from 9 million in 2010 to 33.8 million in 2020, per the U.S. Census . The multiracial population is expected to keep growing faster than most groups, and exactly how fast depends as much on how America measures race as how it lives or understands it. Zoom in: Before the 1960s, race was often assigned by census takers. Today, it's largely self-identified. The U.S. Census now allows people to "mark one or more" races. People often change how they identify over time and across contexts, experts say. A multiracial respondent may identify as two races in one survey but as just one in another. Friction point: The same population can produce different answers depending on how race is measured.…