The Percent Changes in Violent Crime Under Biden are Statistically Significant at the better than the 0.0001% Level for a Two-tailed t-statistic

Despite what the media and the Bureau of Justice Statistics are noting, if you look at the percentage changes in crime rates under the Biden administration, there has never been such a large increase in felonious violent crimes. Indeed, nothing even close. Outside of the 55.4% increase in 2023 over 2020 and the increase in 2022, the next largest increase was the 27% increase in 2006 over 2003. And that increase in 2023 is extremely statistically significant. While researchers might use levels of significance at the 5% or 10% level, these percentage changes from 2020 to 2023 or from 2019 to 2023 are significant at better than the 0.0001% level. The same is true if one includes simple assaults, which are misdemeanors.

UPDATE: Friday, the Associated Press put out another attack on Trump’s claims about crime.

CLAIM: New numbers show that crime has skyrocketed under the Biden administration.

THE FACTS: Violent crime surged during the pandemic, with homicides increasing nearly 30% in 2020 over the previous year — the largest one-year jump since the FBI began keeping records.

But FBI data released in June shows that the overall violent crime rate declined 15% in the first three months of 2024 compared to the same period last year. One expert has cautioned, however, that those figures are preliminary and may overstate the actual reduction in crime.

On Friday, Trump cited numbers he said were from the “bureau of justice statistics” to claim crime was up. This appears to be a reference to the National Crime Victimization Survey recently released by the Justice Department, which shows that the number of times people were victims of violent crime increased by about 40% from 2020 to 2023. The report notes, however, that while the rate of violent victimizations in 2023 was higher than it was in 2020 and 2021, it was not statistically different from the rate in 2019, when Trump was president.

Melissa Golden, “FACT FOCUS: A look at false claims made by Trump in California,” Associated Press, September 13, 2024.

1. The increase from 2020 to 2023 in violent crime (rape, robbery, and aggravated assaults) was 55.4%. That is the largest percentage increase in violent crime over any three years recorded by the NCVS. The increase from 2019 to 2023 was 19.2%, the second largest increase in violent crime over any four years by the NCVS. The largest increase was in 2006. Excluding simple assaults (which is a misdemeanor) includes the same violent crimes included in the FBI measure of violent crime since they only include felonies. If you use the data with misdemeanors, the change from 2020 to 2023 was 37.2%, and from 2019 to 2023, just 7.1%. The 7.1% increase is much smaller than the 19.2% increase in felonies. Understandably, people will focus on the large percentage increases in felonies.
2. Trump stated that crime increased under the Biden administration. Golden responds by saying the change from 2019 (using the misdemeanor numbers was up) was not statistically significantly different from 2023. The percentage increases were statistically significant, using the crimes analogous to the FBI’s violent crime data.
3. The “Three Years Differences” variable compares the percent change from 2020 to 2023 to all the other three-year changes in the NCVS data. The “Four Year Difference” compares the percent change from 2019 to 2023 to all the other four-year changes in NCVS data. The first two estimates look at the total violent crimes for rape, robbery, and aggravated assault. The second two estimates look at the total violent crimes for rape, robbery, aggravated assault, and simple assault. The percentage crime rate increases during the Biden administration were all statistically significant, at least at the 0.0001 percent level, for a two-tailed t-test. These comparisons were made removing the value for 2023 from the comparison sample, but the results are unchanged if it is included. The STATA date file is available for download here.

4. While it is obvious why Americans might focus on the percent changes instead of the levels, over the last twenty years, even looking at the levels, the increase in violent felonies between 2020 and either 2022 or the last two years of the Biden administration was statistically significant at the 7% level. There were large drops in crime levels during the 1990s but no increases. However, including those large drops in the levels, because they are such large drops, makes it more difficult to find that the rise is statistically significant. Finally, while there was an increase from 2019 to the last two years of the Biden administration, it wasn’t statistically significant whether one looks at the last twenty years or includes the drops during the 1990s.