Handcuffing the Cops: Miranda's Harmful Effects on Law Enforcement

Policy Reports | Crime

No. 218
Saturday, August 01, 1998
by Paul G. Cassell

Confirming the Effect on Clearance Rates

Figure V - Individual Violent Crime Clearance Rates

"Standard statistical techniques also show that the Miranda decision was the primary cause of the drop in crimes solved."

As theory and contemporaneous police reports suggest that the Miranda decision was a primary cause of the 1966 to 1968 drop in clearance rates, so do standard statistical techniques. The generally accepted device for sorting through competing possibilities is multiple regression analysis.

The Regression Model. The first step in developing a regression model is to identify relevant variables for the equations. For our dependent variable, Professor Fowles and I used clearance rates at a national level based on FBI data.28 For control variables, the factor most commonly cited as affecting the clearance rate is the crime rate. The standard argument is that as police officers have more crimes to solve, they will be able to solve a smaller percentage of them. Apart from the crime rate, the most often cited factors influencing clearance rates are law enforcement officers and expenditures on law enforcement. To control for such influences, we added variables for the number of law enforcement personnel per capita and the dollars spent on police protection per capita by state and local governments, adjusted for inflation by the consumer price index. We also controlled for the interactions between these variables and the overall number of crimes-what has been called the "capacity" of the system.29

Other variables have been identified in the criminal justice literature as having some bearing on clearance rates or, more generally, crime rates. We controlled for the percentage of juveniles in the population, the unemployment rate, disposable per capita real income, labor force participation, live births to unmarried mothers, levels of urbanization and the distribution of crimes committed in large and small cities. Finally, to capture the effects of the Miranda decision, we included a "dummy" variable in the equations. This was assigned the value of 0 before Miranda, + in the year of Miranda (1966) and 1 thereafter.

Miranda's Significant Effect. The findings, detailed in Appendix Table I, are that Miranda had a statistically significant effect on clearance rates for both violent and property crimes.

  • The coefficient associated with the Miranda variable implies that violent crime clearance rates would be 6.7 percentage points higher without Miranda.
  • The coefficient associated with the Miranda variable indicates that property crime clearance rates would be 2.2 percentage points higher.

In 1995 the violent crime clearance rate was 45.4 percent and the property crime clearance rate 17.7 percent:30

  • The regression equations suggest that without Miranda the violent crime clearance rate would have been 50.2 percent (43.5 percent + 6.7 percent).
  • The equations suggest that the property crime clearance rate would have been 19.9 percent (17.7 percent + 2.2 percent).
Figure VI - Robbery Clearance Rates

The Effect on Clearing Individual Crimes. These findings are for the total categories of "violent" and "property" crime. There is a danger, of course, that such aggregations may obscure what is happening in individual crime categories. For this reason, we ran separate regressions on the individual violent and property crimes. Figure V depicts clearance rates for the violent crimes of homicide, rape and aggravated assault. Figure VI depicts the clearance rate for robbery (shown separately because its clearance rate is so much lower). Except for robbery, all exhibit a long-term downward trend, but not a sharp downward break in the 1966 to 1968 period.

"Miranda had a significant effect on robbery clearances but not on other violent crimes."

The sharp reduction in robbery clearances shown in Figure VI suggests that robbery clearances are the most likely to be affected by Miranda. The results of the regression analyses [see Appendix Table II] confirm that Miranda had a significant effect on robbery clearances but not on other violent crimes.

Clearances of property crimes (burglary, larceny and vehicle theft) all exhibit a long-term downward trend, as Figure VII shows. Larceny and vehicle theft clearances show particularly sharp drops in the 1966 to 1968 period, while the sharp drop in burglary clearances extends from 1961 to 1968. These visual observations track the regression results [reported in Appendix Table III]. The Miranda variable has a statistically significant downward effect on clearance rates for larceny and vehicle theft. For burglary, the Miranda variable is not statistically significant at the conventional 95 percent confidence level (but is significant at a 90 percent confidence level).

"The percent of property crimes solved all exhibit a long-term downward trend."

The regression equation controls for two of the factors cited in the Uniform Crime Report as possible reasons for the clearance rate decline: the increase in police workloads and the static ratio of police strength. Increased mobility of those committing crimes is possible, but seems an unlikely explanation for a sudden, three-year shift in crime clearance rates. Increasing mobility could affect clearances only over the long haul. That leaves the first factor - "court decisions which have resulted in restrictions on police investigative and enforcement practices" - as the logical candidate for explaining the sudden drop in clearance rates.

Figure VII - Clearances of Individual Property Crimes

The Range of the Miranda Effect. Having considered various models for the Miranda effect, we set out a short summary of our findings and the range of the possible effect of the decision on clearance rates. Table I displays the pertinent information.

"Without Miranda, between 8,000 and 36,000 more robberies would have been solved in 1995."

The first column sets out the clearance rate for the various crime categories for 1995 - for example, a 24.2 percent clearance rate for robbery. The second column shows the range of the Miranda effect found in considering all possible combinations of the variables in our equations.31 For example, depending on the model specification, robbery clearances were somewhere between 1.6 and 7.2 percentage points lower, depending on what variables one includes or excludes. To provide some context for these figures, the third column sets out the rate at which clearances would have increased without the Miranda effect. For example, given that only 24.2 percent of robberies were cleared in 1994, increasing the clearance rate by 1.6 to 7.2 percentage points would have meant the clearance of 6.6 percent to 29.7 percent more robberies. Because of interest in the absolute number of crimes affected, we estimate in the last column how many more crimes would have been cleared in 1995 in the absence of the Miranda effect. Our equations suggest, for instance, that without Miranda between 8,000 and 36,000 more robberies would have been solved in 1995. It should be emphasized again that these estimates are quite conservative. They capture only Miranda's impact on crime clearances, ignoring some of the effects on prosecutions and convictions at later points in the criminal justice system.

Explaining the Pattern. Our equations suggest a Miranda effect on clearance rates for robbery, larceny and vehicle theft (and possibly burglary), but not homicide, rape and assault. What could explain this pattern? No doubt the reasons are complex, but reasonable possibilities suggest themselves.

What might be called crimes of passion or emotion - murder, rape and assault - were apparently unaffected by Miranda, while crimes of deliberation - robbery, larceny, vehicle theft and possibly burglary - were affected. These categories are oversimplifications; obviously there are coolly calculated murders and impulsive car thefts. But if the generalizations are more often correct than incorrect, they correspond with the larger body of evidence suggesting that Miranda more substantially affects police success in dealing with repeat offenders and professional criminals.32

Table I - Summary of the Range and Size of the Effect of the Miranda Variable

"Police clear some kinds of crime through confessions more often than others."

Still another explanation is that police may more often clear some kinds of crimes through confessions. A study of the New York City Police Department around the time of Miranda reported widely varying ratios of clearances to arrests across crime categories.33 The ratio of clearances to arrests is well in excess of 1 for some crimes - specifically burglary, grand larceny, grand larceny vehicle and robbery. Police might arrest, for example, a professional burglar who would confess not only to the burglary for which he was apprehended, but to several he had previously committed. For other crimes-specifically homicide, rape and assault-the ratio was quite close to 1. This suggests that confessions may play a more important role in clearances of such crimes as burglary, vehicle theft, larceny and robbery, and thus clearance rates for these crimes are more susceptible to changes in confession procedures.

Another possibility is resource shifts by police to maintain high clearance rates for the most serious and less numerous crimes such as murder or rape. After Miranda, police may have responded to the difficulties created by the Supreme Court by reassigning some officers to the homicide division. Police agencies are frequently judged by their effectiveness in solving the most notorious crimes, especially murders. This transfer of resources would produce lower clearance rates for less visible and more numerous crimes like larceny or vehicle theft.

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