The federal government tries to track this subset of the population with databases like the National Vital Statistics System, which is based on death certificates. As public attention on police violence has increased in recent years, media organizations began making databases of their own—like the Guardian's The Counted or the Washington Post's Fatal Force—to track law enforcement-related deaths. Comparisons between the data sets suggested that the official government data was severely undercounting police-related deaths. However, no one really knew how accurate those media databases were either. [...]
The researchers matched cases of police-related deaths from NVSS mortality records and The Counted, and used a statistical tool called capture-recapture analysis to estimate the number of cases missing from both data sets. Wildlife ecologists often use this technique to estimate the size of a wild population. They'll trap animals, tag and release them, and then try to trap them again. "With this method, if you have two ways of collecting data, you look at to what degree do they overlap," says Justin Feldman, a doctoral candidate at the Harvard T.H. Chan School of Public Health and lead author on the new study. If there's not a lot of overlap, the estimate of uncounted animals—or, in this study, cases of police-related deaths—would be large, Feldman explains. Conversely, a large amount of overlap would lead to a small estimate of uncounted cases. [...]
In 2015, the NVSS recorded 523 law enforcement-related deaths, while The Counted identified 1,086 such cases. There was significant overlap between the two sources, according to the new study; 487 cases appeared in both lists. From this data, the authors estimated that at least 1,166 people were killed by police in the U.S. in 2015. The news-based system counted over 93 percent of the deaths, while NVSS captured less than 45 percent.
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