What California Counties are Arresting Juveniles at Abnormally High Rates?

A new analysis by the San Francisco Brigade’s Data Science Working Group shows that three California counties have a repeated pattern of arresting juveniles of certain ethnicities at an abnormally high rate compared to the rest of the state.

Two of them – San Francisco and Marin counties – are a surprise, as they make up part of the progressive Bay Area.

One might expect the region’s liberal ideology to be reflected in the juvenile criminal justice system. Juvenile criminal justice is an area that has received more attention in recent years; activists have highlighted issues like racial disparities in policing and the school-to-prison pipeline. If California’s progressive counties were making progress in tackling these issues, we would hope to see a smaller proportion of youth being caught up in the criminal justice system there than elsewhere in the state.

However, the newly analyzed data suggests the opposite. We found three counties in California that have had a history of abnormally high arrest rates for juveniles of certain ethnicities: San Francisco and Marin counties in the Bay Area, and Kings county in the Central Valley. Furthermore, the two Bay Area counties have abnormally high youth arrest rates specifically within their black and Hispanic communities. All three of these counties deserve further scrutiny to better understand why young people there are more likely to be arrested than they would be if they lived in another part of the state.



These findings were made by the San Francisco Brigade’s Data Science Working Group. The analysis was based on juvenile arrest data from 1994 to 2014 released by the California Department of Justice through their OpenJustice initiative. This data gives an unprecedented view into California’s criminal justice system and the racial and regional inequities that exist within it.

To analyze the data, we grouped the arrests by year, ethnicity, offense level, and county, then combined it with the county’s relevant population to calculate a per capita arrest rate. This gave us 4,616 arrest rates, each one measuring the arrest rate for a certain ethnic group, year, offense level, and county. We used this dataset to create distribution curves that compare each type of arrest rate between counties. Finally, we identified the instances where a particular county’s arrest rate for that group is an outlier (i.e., it’s arrest rate is more than 3 standard deviations above the mean).

For example, in 2014, we know the arrest rates of white youth from 34 California counties. On average, each of those counties made 4 misdemeanor arrests of juvenile white suspects for every 1,000 white juveniles who live in the county. However, Kings County made over 15 such arrests, while no other county made more than 11. By creating a distribution of all 34 arrest rates, we can confirm statistically that this is an abnormally high arrest rate (here, Kings County’s z-score is 3.8).

We found 89 of these outliers: times where a county stood out from the rest because of their unnaturally high arrest rates for a particular ethnic group and offense level in a certain year. 69% of those abnormalities occurred in just 3 counties: 27 in SF, 21 Kings, and 13 in Marin. While this is not conclusive proof of a racial disparity in those counties, it raises red flags about juvenile arrest practices in those counties.

County Level Details

San Francisco County’s data is the muddiest, due to known issues in how the ethnicity of arrested suspects is recorded. For years, Hispanic arrestees were listed as white, and Asian arrestees were listed as “other”. This miscoding throws off the accuracy for each of those four groups. The unreliability of data in these groups means that we should exclude them from the results, which explains 19 of the 27 times that San Francisco County’s arrest rates are an outlier.

However, the other 8 outliers are quite concerning: black juveniles have been arrested for felonies at disproportionately high rates in SF compared to in other counties. The black felony arrest rate was an outlier In all but two years from 2005 to 2014. While the offense level here reflects the original arrest, not the charges officially filed by the District Attorney, the potential seriousness of these crimes make it particularly concerning that they are occurring abnormally often in SF’s black juvenile population.

Marin County has regularly arrested its Hispanic and black juvenile population at a rate higher than other counties. For example, Marin had 3.5 felony arrests of Hispanic youth for every 1,000 such residents in 2011, which is almost triple the state average. This abnormally frequent arresting was especially true for misdemeanors but has also occurred for felonies and status offenses. The misdemeanor arrest rate for black youth was an outlier in 2005-2007. While the arrest rate for African Americans has since fallen back into proportion with the rest of the state, the arrest rate for Hispanic juveniles remains a concern. The Hispanic arrest rate has been an outlier for felonies in one year (2011), misdemeanors in 5 years, and status offenses in 4 years, including 2014, the most recent year in our dataset.

Finally, Kings County’s arrest rates are disproportionately high in every examined ethnic group at least once. Of the 21 times it appears as an outlier, 1 time is for felony arrests, 8 are for misdemeanors, and 12 are for status offenses. For example, in 2014, Kings made a remarkable 27 misdemeanor arrests of Asian/Pacific islander suspects for every 1,000 such residents, while no other county had more than 7 This high arrest rate across ethnicities suggests that the criminal justice system in Kings County may be quicker to arrest youth for their behavior than officials in other counties. Concerningly, 2014 was the first year in which felony arrest rates were disproportionately high (for Asian/Pacific Islander youth), suggesting that the trend may be spreading to more serious crimes as well.

These findings are concerning for San Francisco, Marin, and Kings Counties. These three counties should ask why they are arresting certain juveniles at much higher rates than their peer counties. Local knowledge is integral to better understand this trend, and officials in those counties are well positioned to investigate this further. There is a troubling possibility that they reflect serious problems in how those counties police their youth.