# Lecture 6: Monty Hall, Simpson's Paradox | Statistics 110 | Summary and Q&A

144.9K views
April 29, 2013
by
Harvard University
Lecture 6: Monty Hall, Simpson's Paradox | Statistics 110

## TL;DR

Simpson's Paradox is a phenomenon where aggregated data shows a different trend than individual data, leading to counterintuitive results.

## Key Insights

• 🥺 Simpson's Paradox is a phenomenon where aggregated data can show a different trend than individual data, leading to counterintuitive results.
• 🖐️ Conditional probabilities play a crucial role in understanding Simpson's Paradox as it involves conditioning on specific factors.
• ❓ The Monty Hall problem is a famous example of Simpson's Paradox, where the naive intuition of a 50/50 chance is incorrect when considering conditional probabilities.
• 🍂 Understanding the assumptions and conditioning in a problem can help avoid falling for Simpson's Paradox.

## Transcript

So we're talking about conditional probability, right? We're continuing to do conditional probability. And so today we're gonna talk about a couple of the most interesting famous problems related to conditional probability. First one, a lot of you have seen in some form or other. And that's called the Monty Hall problem, the three door problem. Ver... Read More

### Q: What is Simpson's Paradox?

Simpson's Paradox is a phenomenon where aggregated data shows a different trend than individual data, leading to counterintuitive results.

### Q: Can you provide an example of Simpson's Paradox?

An example of Simpson's Paradox is when one doctor has a higher success rate in each type of surgery, but the other doctor has a higher overall success rate. This shows that aggregating data can lead to different conclusions.

### Q: How does the Monty Hall problem illustrate Simpson's Paradox?

The Monty Hall problem is a famous example of Simpson's Paradox. Initially, it may seem that switching doors has a 50/50 chance of success, but when considering conditional probabilities, it is more beneficial to switch, leading to a different result.

### Q: Why does Simpson's Paradox occur?

Simpson's Paradox occurs because conditioning on certain factors can change the probabilities and lead to unexpected results when aggregated.

## Summary

This video discusses two famous problems related to conditional probability: the Monty Hall problem and Simpson's paradox. The Monty Hall problem is a game show problem where you have to choose a door and decide whether or not to switch doors based on new information. The video explains the correct strategy and demonstrates how it leads to a higher probability of success. Simpson's paradox, on the other hand, is a phenomenon where the direction of an inequality flips when data is aggregated. The video provides examples and explains the mathematical reasoning behind Simpson's paradox.

### Q: What is the Monty Hall problem?

The Monty Hall problem is a game show problem where you have to choose a door and decide whether or not to switch doors based on new information. It involves assumptions about the location of a car and two goats behind the doors and the knowledge of Monty Hall, the game show host.

### Q: Why is the Monty Hall problem considered a paradox?

The Monty Hall problem is considered a paradox because the correct strategy, which is to switch doors, goes against intuition for many people. It seems counterintuitive that switching doors would increase the probability of winning, but it is actually the optimal strategy.

### Q: What assumptions are made in the Monty Hall problem?

The assumptions in the Monty Hall problem include: one door has a car, the other two have goats; the contestant has no knowledge of which door has the car; Monty Hall knows which door has the car; Monty Hall always gives the option to switch; and Monty Hall opens a door with a goat, not the car.

### Q: What is the strategy for the Monty Hall problem?

The optimal strategy for the Monty Hall problem is to always switch doors. This is because switching doors increases the probability of the car being behind the chosen door from 1/3 to 2/3.

### Q: How can the Monty Hall problem be explained using probability trees?

A probability tree is a useful way to visualize and understand the Monty Hall problem. By drawing out the different possibilities and their probabilities, it becomes clear that switching doors leads to a higher probability of success.

### Q: What is Simpson's paradox?

Simpson's paradox is a phenomenon where the direction of an inequality flips when data is aggregated. It occurs when a certain pattern holds for individual groups but is reversed when the groups are combined.

### Q: Can you give an example of Simpson's paradox?

One example of Simpson's paradox is with two doctors who have different success rates for different types of surgeries. Despite the first doctor having a higher success rate for every type of surgery individually, the second doctor has a higher overall success rate when the surgeries are aggregated.

### Q: How can Simpson's paradox be explained using conditional probability?

Simpson's paradox can be understood using conditional probability by examining the probabilities of success given certain conditions. Comparing the probabilities of success for different conditions may lead to contradictory conclusions when aggregated.

### Q: What is the confounder in Simpson's paradox?

The confounder in Simpson's paradox is a variable that affects both the outcome and the treatment assigned, leading to misleading conclusions when the groups are combined.

### Q: What are some real-life examples of Simpson's paradox?

Some real-life examples of Simpson's paradox include a court case involving sex discrimination in graduate admissions at UC Berkeley and the difference in batting averages between two baseball players.

## Takeaways

The Monty Hall problem and Simpson's paradox both demonstrate the importance of understanding conditional probability and the potential for counterintuitive results. The Monty Hall problem shows that switching doors can increase the chances of winning, while Simpson's paradox highlights how the aggregation of data can lead to reversed inequalities. It is crucial to consider all relevant factors and condition on confounders when analyzing data and making decisions.

## Summary & Key Takeaways

• Simpson's Paradox occurs when individual comparisons show one result, but when aggregated, the result flips. For example, one doctor may have a higher success rate in every type of surgery, but the other doctor has a higher overall success rate.

• The Monty Hall problem is another famous example of Simpson's Paradox. Initially, it may seem that switching doors has a 50/50 chance, but when considering conditional probabilities, it is more beneficial to switch.

• The paradox can be explained by the fact that conditioning on certain factors changes the probabilities, leading to unexpected results.