Denver Bullet Study

This post is largely a continuation of the Kenneth R Hammond post, but one prompted by recent current events. My opinion on gun control is probably readily apparent. But if it is not, let me say that I go crazy when mental health is bandied about as the reason for our school shootings or when we hear that  arming teachers is a solution to anything. However,  going crazy or questioning the sincerity of people with whom you are arguing is not a good idea. Dan Kahan (See my posts Cultural Cognition or Curiosity or his blog Cultural Cognition) has some great ideas on this, but Ken Hammond actually had accomplishments and they could help guide all of us today. I should note also that I was unable to quickly find the original sources so I am relying completely on: “Kenneth R. Hammond’s contributions to the study of judgment and decision making,” written by Mandeep K. Dhami and Jeryl L. Mumpower that appeared in  Judgment and Decision Making, Vol. 13, No. 1, January 2018, pp. 1–22.

In 1974, the Denver Police Department (DPD) decided to change its handgun ammunition because it was argued that conventional round-nosed bullets provided insufficient ‘stopping effectiveness’ (i.e., the ability to incapacitate and thus to prevent the person shot from firing back at the police or others). The DPD chief recommended using a hollow-point bullet, claiming that such bullets flattened on impact, thus decreasing penetration, increasing stopping effectiveness, and decreasing ricochet potential. This claim was challenged by, for example, the American Civil Liberties Union and minority groups. Opponents stated that
the new bullets were in fact outlawed ‘dum-dum’ bullets which were more injurious than the round-nosed bullet and so should be barred from use. There were public hearings, debates and disputes, and appeals by both sides to ballistics experts for scientific information and support. Disputants focused on evaluating the merits of specific alternative bullets—
confounding the physical effect of the bullets with social policy implications.


According to Dhami and Mumpower, Kenneth Hammond and Leonard Adelman realized that the disputants confounded questions of value — what the bullet should accomplish with questions of fact — concerning ballistic characteristics of specific bullets. Arguments favored one option or another, but obscured the basis for a preference. In their work, Hammond and Adelman stated that policy makers inadvertently had adopted the role of (unqualified) ballistics experts, and ballistics experts inadvertently had adopted the role of (poor) policy makers. Hammond and Adelman intervened to first discover the important policy dimensions from the policy makers’ viewpoint and then elicited ballistics experts’ ratings of the bullets on these dimensions. The relevant dimensions were stopping effectiveness, probability of serious injury, and probability of harm to bystanders. The experts’ ratings of the bullets on the last two dimensions were almost perfectly confounded. The probability of serious harm to bystanders is highly related to the penetration of the bullet, whereas the probability of the bullet effectively stopping someone from returning fire is highly related to the width of the entry wound. Giving equal weights to these dimensions, and combining these weights with the experts’ technical judgments, led Hammond and Adelman  to identify a bullet that “has greater stopping effectiveness and is less apt to cause injury (and is less apt to threaten bystanders) than the standard bullet then in use by the DPD.” The bullet they recommended was accepted by both the DPD and the Denver City Council and put into operation.

According to Leonard Adelman the  study illustrated the significant contribution of Hammond’s Social Judgment Theory in identifying the importance of the “separation of facts and values” in resolving social policy disputes. Adelman identifies five key points to be derived from the Denver Bullet Study. First, social polices comprise three types of judgments: (a) value judgments about what ought to be, (b) factual judgments about what is or will be, and (c) evaluative
judgments that integrate value and factual judgments into a final policy decision. Second, policy makers should be responsible for value judgments and technical experts for factual judgments. Third, methods exist to build quantitative models for both value and factual judgments. Fourth, analytical methods can and should be used to combine value and factual judgments so that alternatives can be systematically evaluated. Fifth, cognitive feedback can be used to make
the implications of value judgments and factual judgments explicit.

A couple of other posts come to mind that might help us make better decisions with this sort of issue. See post Slippery Slope and Slippery Slope Hypocrites.   We tend to put arguments in different categories based on who is saying them, the strength of the arguments, and quite possibly the reference point which we are using. This might cause a kind of parallax.  It also points out something most of us already know, putting ourselves in someone else’s shoes can explain a lot that we often ignore.



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