Explore ways that groups fall short of their optimal reasoning ability. There are better and worse ways to aggregate a group's knowledge.
This lesson discusses when groups of people make better or worse judgments than individuals. It leads into the last part of the course, which revolves around group decision making, e.g. as a society.
After this lesson, students should
Wisdom of Crowds
Herd Thinking
Meta-analysis
Family Dynamics
Congressional Committees
Scientific Community
Everyone agrees, so it must be true.
I trust my guess about how many pages are in this book more than the average of my guess with other people's guesses, because even if I don't have more information than other people, it's MY guess and you should stick with your own guess.
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Bias in Jurors vs Bias in Juries: New Evidence from the SDS Perspective
On jury bias and composition. Kerr, Niedermeier and Kaplan, 1999.
The Social Psychology of the Wisdom of Crowds
Richard Larrick, Albert Mannes, and Jack Soll on the wisdom of crowds.
Update the Google form in the warm-up polls.
| 5 Minutes | Introduce the lesson and go over the plan for the day. Make sure people have groups, spokespeople, etc. |
| 30 Minutes | Have the class do the assorted warm-up polls. |
| 40 Minutes | Walk the class through the various jury discussions. |
| 5 Minutes | Do the group problem if time allows. This part is optional. |
For this discussion section, students will start by filling out a Google form which asks for their best estimate of four quantities (should take 3-5 mins). The form should connect to a spreadsheet which shows how the class is or isn't aggregating live. Depending on the particular setup, this may take some spreadsheet finagling live during class. An example spreadsheet that was used in spring 2023 can be found below.
This first poll demonstrates the wisdom of crowds and what happens when there's a systematic bias in people's judgments. It has the following four numerical questions.
922 lbs
166 lbs
55 lbs
163 lbs
Make sure to copy the Google form and provide it to the students with a link and/or QR code.
Make sure the students give their best guesses for each question without discussing with any classmates or looking any answers up. Don't reveal the answers until everyone's submitted their responses.
This poll demonstrates the power of herd thinking in amplifying shared biases. Students are shown the painting on the right and asked which of the following artists created it.
Note that the names are ordered this way so that Claude Monet gets asked before Armand Guillaumin. If the order is switched you may get an opposite effect where a slightly larger (or more confident) proportion of students voting for Armand Guillaumin inspires more students to herd with them. In this case, the power of expertise directing a group is demonstrated.
The poll is done in two rounds. In both cases, say the names in order and count how many students raise their hands for each one. Pause for a moment to give students a chance to get their hands up if they're slow (and to see what other people are doing).
The correct answer is Armand Guillamin. However, it's likely the case that most people will pick Monet, because he is more widely known than the other options. This is an example of the negative outcome of herd thinking, where a group of people independently and collectively select the wrong answer because they all share the same prior bias (picking the famous painter). In the first case the bias only comes from people's tendency to pick familiar names. In the second, it may get amplified by seeing other more people raise their hands and then wanting to join in.
This activity often does not work as intended. Students usually understand what it's intending to convey, but it's hard to get them to fall victim to it within the classroom.
Students may not know what a starling murmuration is unless you show/tell them.
The final warm-up is a quick poll (via hand raising is fine) to ask the students what the best way to answer each of the following questions is. Should it be done by deciding separately and averaging, by discussing as a group, or through some other means?
Independent Guesses.
Group Discussion. It's about a thousand miles below the surface of the Earth.
It's complicated. We will go over this more in the jury discussion next.
Many of the students may be international or haven't served on a jury before. So, we start by giving them a quick reminder of juries' most important features (for the purposes of this course).
We start with some discussion questions about shared biases. These should be answerable given the takeaways from the previous activity. Remind the students that juries typically discuss the merits of the case as a group so as to come to a consensus on whether the defendant is guilty.
Given the dynamics of conformity and obedience, the exact number of people and explicit decision making processes may also play a role in the decisions they make.
Given this, have the students answer the following questions.
Kaplan & Miller (1978): Argued that deliberation helps juries reach a just evaluation of cases by averaging across different biases. The jury does this by arguing/debating the merits of the case. Strong/weak refers to the merits in the figure. The study varied obnoxiousness of attorney and which case was strong. Deliberation helps juries reach a just evaluation of cases by averaging across different biases. (Regardless of how obnoxious the attorney is, as long as they present the evidence.)
Group Polarization: Group deliberation tends to exaggerate shared biases. For example…
MacCoun (1985, 1990): Juries tended to overweight a completely irrelevant consideration: the defendant's attractiveness.
Why did juries overweight attractiveness? Because it's a shared bias.
Kerr, Niedermeier, & Kaplan (1999): Groups magnify biases when evidence is ambiguous. Groups reduce bias when evidence is really strong or weak.
Bias in Jurors vs Bias in Juries: New Evidence from the SDS Perspective
On jury bias and composition. Kerr, Niedermeier and Kaplan, 1999.
Have the students discuss the following in small groups.
There's no one canonical answer to these questions. But, encourage the students to be really creative. Their solutions may include things like having multiple juries and judges debating in parallel, having the attorneys not know which side they're going to defend until the start of the trial, trying to find other ways to blind the jurors to irrelevant aspects of the case, etc.
The purpose of this is just to give one last final example of a case in which having group deliberation does help. Typically one person figures out the trick and everyone else understands once it's explained.
Jack is looking at Anne, but Anne is looking at George. Jack is married, but George is not. Is a married person looking at an unmarried person?
Explanation
The correct answer is the first one. But, most people think it can't be determined. Consider the two cases. Either Anne is married or they're not. If Anne is married then Anne looking at George is the case of a married person looking at an unmarried person. If Anne is not married then Jack looking at Anne is the case of a married person looking at an unmarried person. Either way, it happens.
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