Police resources and crime solving: A closer look at clearance rate trends in California

A recent report by the Center on Juvenile and Criminal Justice (CJCJ) tried to take a stand by exposing poor clearance rates of California law enforcement agencies. They specifically argue that police staffing levels and police spending do not translate to improved clearance rates and actually increase crime.

While clearance rates are an important metric for measuring police effectiveness, the conclusions of the CJCJ report are questionable because the analysis lacks depth and overlooks critical factors related to clearance rates. In this post, I’ll provide additional context to offer a more balanced perspective on the relationship between police resources, clearance rates, and crime rates.

The CJCJ Analysis

The first major claim made in the report is that “California’s police and sheriff departments are spending significantly more money and solving far fewer crimes than they did decades ago.” They cite the California DOJ data and discuss how clearance rates have dropped from 22.3% to 13.7% between 1990 and 2023, “despite unprecedented funding levels.” The CJCJ report goes on to explain that inefficient law enforcement is really to blame for increased crime and declining clearance rates, stating that “increased police department funding is associated with worse crime-solving and more crime.” In an attempt to illustrate this point, the author displays a series of graphs and tables highlighting data on law enforcement personnel and funding.

According to the data in the report, the number of sworn officers and deputies per capita has decreased slightly since 1990, while the total number of law enforcement personnel has increased by just 0.7%, and spending has surged by 46%. During the same time, clearance rates have decreased by 41%. But as shown in the graph below, this varies by type of crime and is not necessarily the most straightforward trendline.

Source: California DOJ Data

While I agree that declining clearance rates is something that warrants concern, I believe that it’s overly simplistic to attribute this decline to any one factor in particular. In addition, it’s important to note nuances within the data. For example, clearance rates are actually trending upward for both robbery and homicide. But overall, the clearance rate trends are not completely straightforward, with a lot of ebb and flow over the years. Since 2021, clearance rates have remained relatively stagnant for most crimes except for homicide, which has seen a steady incline in clearance rates from 2021 through 2023.

In the Appendix of the CJCJ report, the author reveals several correlation coefficients comparing clearance rates and officers per capita. The correlation coefficients reveal a very weak association between clearance rates and officers per capita; the correlations are so miniscule they are essentially meaningless, ranging from 0.078-0.163 on a scale from 0.0-1.0. It’s also important to note that correlations do not account for temporal order, and it’s not possible to know whether the low clearance rates led to the hiring of more officers or vice versa. The authors also use weak correlation coefficients as support for the claim that police spending and staffing levels were positively correlated with crime rates. Once again, this is not necessarily true. While there is a correlation between police spending and crime rates, there is no indication of temporal order. It’s just as likely that high crime rates led to higher police spending rather than the other way around.

Overall, it’s unclear why the author used a series of correlations as the main method of analysis, as opposed to other statistical tests that can do so while also accounting for temporal order. There are many factors that impact clearance rates, and the CJCJ analysis is too simplistic to get a firm understanding.

Oversights

Shockingly, the author neglects to mention the importance of having specially trained detectives and skilled forensics teams to perform investigations, which plays a very large role in improving clearance rates. The author simply highlights numbers of law enforcement staff and numbers of sworn officers without providing any breakdown regarding what percentage of officers are detectives or whether any of them are specially trained in forensics. Contrary to popular belief, the patrol cops that are doing everyday beat patrol are not going to be the same ones investigating crimes, so the number of patrol cops would not necessarily impact clearance rates. Therefore, simply looking at the number of officers and number of staff doesn’t provide enough context regarding the trends in clearance rates. This analysis really needed more detail about how the sampled agencies conduct investigations and what their personnel training looks like.

For example, research conducted in Boston, Massachusetts (BPD), and Rochester, New York (RPD), suggests that departments are capable of improving their homicide clearance rates. Both departments implemented a series of reforms, which included hiring additional staff to support homicide investigations. BPD hired a civilian crime analyst, a victim witness resource officer, and eight additional detectives for their homicide unit, while RPD hired seven new investigators as well as other personnel to assist in completing tasks such as writing search warrants, obtaining CCTV video, and interviewing witnesses. Both departments increased supervisory oversight of investigations through regular progress meetings and peer review sessions for open investigations. BPD also revamped the training for their homicide, forensics, and crime scene response units, and they began deploying the forensics unit to homicide scenes to ensure adequate collection and storage of evidence. After making these improvements, BPD saw about a 10% increase in their clearance rates, while RPD saw a 29% increase. This held across case types, including particularly challenging circumstances such as gang- and drug-related cases. Overall, it seems that increasing staff and providing additional support to police investigative units can actually help improve clearance rates, contrary to CJCJ’s conclusion. But it’s not just the sheer number of officers or staff that matters. What really matters is whether they have the time and skills required to perform thorough investigations. Obviously, a boost in investigative quality makes cases easier to solve and therefore impacts clearance rates.

These concepts extend beyond homicide as well. For example, a study from Tucson, Arizona, revealed that investigative thoroughness was the primary factor affecting burglary clearance rates. The authors found that burglaries involving forced entry were more likely to be solved due to the fact that they had more physical evidence. These cases tend to be investigated more thoroughly for two reasons. First, evidence generates potential leads or can be used to link a suspect to a crime. Subsequently, this enhances the perceived “solvability” of the case. Usually, the more “solvable” cases are prioritized and thus are more likely to have a detective assigned. Not surprisingly, this significantly affects which cases are more likely to be cleared.

Discussion

Investigative quality tends to be the driving predictor of case clearance, though obviously this can be influenced by many factors such as forensic evidence (e.g., DNA, fingerprints), digital evidence (e.g., CCTV, mobile phone data), and evidence from witness statements. But it also requires that staff and detectives are able and willing to put forth the time and effort to investigate. They have to properly collect and store the forensic evidence, download and analyze cell phone and digital records, collect and review CCTV footage, interview neighbors and obtain witness statements, and more. This is not something that happens passively or quickly, which is why having a pool of experienced detectives can boost clearance rates. Similarly, having a good forensics unit also helps.

But police are not a monolith, and jurisdictions operate differently. Likewise, an investigator’s role depends a lot on how the agency conducts investigations and how its efforts are organized. Some enforce strict requirements for investigations, while others have no oversight process at all. Neighborhoods also operate differently, which can sometimes hinder investigations despite best efforts. Following up and engaging with witnesses can sometimes be difficult in neighborhoods where there is low trust in the police, as an example. Considering the large variation between agencies, we can also expect wide variation in clearance rates. To really understand where more work is needed to boost clearance rates overall, we would need to look more closely at individual departments.

Conclusion

While the CJCJ report raises valid concerns about declining clearance rates and the relationship between police funding and crime, its analysis is ultimately insufficient. The simplistic correlation between funding, staffing levels, and clearance rates overlooks important factors such as investigative quality, specialized training, and community dynamics, all of which play crucial roles in determining clearance outcomes. As demonstrated in various police departments, improving clearance rates requires a multifaceted approach that includes not just increasing personnel but also enhancing the skills and resources available to detectives and investigative units. A nuanced understanding of these dynamics is essential for actually increasing clearance rates and reducing crime.