A natural experiment is one where a control group and an experimental group arise naturally without intervention by an experimenter. The use of a natural experiment was reinvigorated by the work of Alan Krueger, who used this technique to study economics. Currently, a natural experiment has arisen which can elucidate the effects of punishment on crime.
The Laffer curve relates the revenue that a government receives to the tax rate imposed. Naively, one might believe that a higher tax rate leads to increased revenue. This is only true up until a point. As the following chart shows, the Laffer curve indicates that beyond a threshold tax rate, increasing taxes decreases government revenue.
This phenomenon is easily explained when we consider the extreme tax rates. A tax rate of 0% would yield revenue of $0. If the government were to tax all income then there would be no benefit to work, nobody would work, and the government would again attain $0 revenue. It is well known that a modest tax rate yields government revenue. With an assumption of continuity, the Laffer curve is revealed.
One might ask whether there is an analogous phenomenon relating the amount of crime to the amount of punishment. Perhaps punishment could be so extreme that if the punishment is reduced then the amount of crime is reduced. This was the hypothesis of several recently elected District Attorneys who proceeded to reduce the amount of punishment for specific crimes.
As an example, the following video shows a woman walking with her baby who was run down by a driver in a stolen car in Los Angeles on 8/6/2021 [1].
The 17 year old who committed the crime, who was previously convicted of felony poisoning, pleaded guilty to two felony counts of assault by means of force likely to produce great bodily harm and one felony count of hit-and-run. He was sentenced to 5-7 months in a juvenile probation camp, described as a place that is a little bit tougher than a summer camp. These minor punishments for serious offenses are typical of those sought by District Attorney George Cascon of Los Angeles during his tenure.
Indeed, several district attorneys in major cities across the United States have pursued similar approaches. These cities include Chicago, San Francisco, Los Angeles, Philadelphia, and Denver. The district attorneys of these cities have been recently appointed, describe themselves as liberal, and have dramatically reduced the punishments for significant crimes [2,3,4]. Actions that previously would have led to arrest are now permitted without consequence. According to the FBI, crime data shows that the number of arrests decreased by 24% [4].
What has been the result? Are we indeed past a critical point where reducing punishment reduces crime? Or is it the case that reducing punishment increases crime?
12 major cities, all with district attorneys who have reduced punishment, exceeded their homicide records in 2021 [4]. In Denver, homicides, aggravated assault, and motor vehicle theft all increased by 10% in 2020. Homicide, assault, human trafficking, and larceny theft all increased in San Francisco in 2021 from between 10% to 25% [5]. A person in San Francisco has a 1/16 chance of becoming a victim of violent crime. At the same time, a person in Miami (led by a conservative district attorney) has a 1/167 chance of becoming a victim of violent crime. Chicago has the same population as Miami; and while the homicide rate in Chicago has increased dramatically, that of Miami has decreased in the same time period [6]. Notably, the number of homicides in New York decreased between June of 2021 and June of 2022 [7]. However, the overall crime index of New York (which include rape, robbery, felony assault, burglary, and grand larceny) increased by 31% during the same time period [7]. Phoenix, Arizona had a significant increase in homicide in 2020, and has not seen a further increase in 2021 [8]. Overall crime has dropped in Phoenix during 2021 [8.1].
Democrat politicians (such as Gavin Newsom) are citing a statistic that Republican states (those that voted for Trump over Biden) have higher homicide rates and more crime than Democrat states [10]. What is not revealed in that statistic, however, is where in the state that crime is happening. It is happening in cities with mayors and district attorneys that have reduced the punishments for violent crimes. For example, though Kentucky voted for Trump over Biden, the governor of Kentucky is a Democrat who permitted the 2020 riots without calling in the National Guard and the mayor and district attorneys of Louisville have reduced punishments on crime. The vast majority of violent crimes in Kentucky are happening in Louisville.
This is all anecdotal; on their own, the facts that I have stated are inconclusive. A statistical analysis would need to be conducted in order to make a conclusion of significance. Notably, the data is there for such a study to be conducted. And at first blush, it sure seems like reducing punishment (and vilifying police) have led to increases in crime.
Finally, I’d like to reveal my opinion. Determining the results of punishments on overall crime statistics is largely irrelevant. Instead, the punishment should fit the crime. Justice, not effect on population, is the main point of relevance. Instead of asking, “What punishment of a person who runs down a woman with a baby in a car would lead to reductions in future crimes?”, I ask the question, “What punishment does a person who runs down a woman with a baby in a car deserve?” Answering the latter question with 5-7 months is distressing. Something on the order of 10, 20, or 50 years seems much more appropriate. This is the approach that Singapore has taken; Singapore is a very safe place.
[1] https://www.foxla.com/news/teen-rammed-car-mother-venice-child-probation
[2] https://www.politico.com/news/2021/04/08/homicide-surge-progressives-district-attorneys-479966
[3] https://www.thecentersquare.com/national/op-ed-progressive-district-attorneys-are-making-our-cities-unsafe/article_da826fda-ab78-11ec-bb94-7366b5c686d5.html
[4] https://abcnews.go.com/US/12-major-us-cities-top-annual-homicide-records/story?id=81466453
[5] https://www.sanfranciscopolice.org/stay-safe/crime-data/crime-dashboard
[6] https://www.miamiherald.com/news/local/crime/article257093332.html
[7] https://www1.nyc.gov/site/nypd/news/p00052/nypd-citywide-crime-statistics-june-2022#:~:text=Overall%20index%20crime%20in%20New,increase%20in%20robbery%20(1%2C548%20v.
[8] https://www.fox10phoenix.com/news/phoenix-homicides-compared-cities-population
[8.1] https://www.12news.com/article/news/crime/police-data-shows-increase-in-some-violent-crimes-in-phoenix/75-99fce62a-5b4b-4503-b83e-49ace5f888ac#:~:text=PHOENIX%20%E2%80%94%20As%20crime%20rates%20surge,31%2C789%20crimes%20reported%20in%20Phoenix.
[10] https://www.salon.com/2022/03/16/democrats-for–but-new-data-shows-higher-rates-in-red-states/
Nicholas Dwork's Blog 
Simple and clear argument in favor of justice. Heartbreaking sorry of mother with stroller.
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