• It’s important to provide a nonpartisan framing for the lesson context. The lesson materials purposefully showcase notable stock trades from representatives on both sides of the aisle. The purpose of this lesson is to analyze stock trades made by all members of Congress – regardless of party. Then, students can generate their own informed opinions about whether members of Congress should be allowed to trade stocks.
• A great way to start this lesson is by asking students what they already know about the stock market. What do they know about how stocks work? Do they know anyone who invests, or have they seen apps where people track their investments? What do they think it means to “own” a stock, and why do people buy them in the first place?
• The lesson currently proceeds in the following order: independence, two-way tables, and the addition rule. The sections on independence and two-way tables directly explore the lesson’s Key Question. So, the current ordering allows instructors to immediately address the Key Question at the beginning of the lesson. Alternatively, instructors could choose to move the section on the addition rule to the beginning of the lesson. This allows for the independence and two-way tables sections to immediately precede (and set up) the Discussion Question. Instructors can choose the ordering that best fits their ideal lesson flow.
• This lesson pulls together several of the key ideas from earlier in the unit, including conditional probability, the multiplication rule, and ways of representing the sample space. It may be helpful to remind students that these concepts are not new, but are now being connected and applied in combination. Continue to emphasize the Keys to Probability as the primary entry point for understanding; the formulas introduced here and in previous sections serve mainly to formalize and support these underlying concepts.

First, download this lesson's Handout Key and read through its Discussion Question section. Then, check out our model discussion norms and the additional background notes below.

• Under current rules, members of congress are allowed to buy and sell stocks, but they are subject to disclosure requirements and restrictions on insider trading. The STOCK Act of 2012 makes it illegal for lawmakers to use nonpublic trading information gained through their official roles for personal financial benefit. The law also requires them to publicly report trades within 45 days. This system emphasizes transparency, but still allows stock trading, which has led to ongoing debate.
• In response to these concerns, Rep. Bryan Steil (R-WI) introduced the Stop Insider Trading Act in January 2026, which would significantly tighten these rules. The proposed legislation would prohibit members of Congress and their immediate family members from purchasing individual stocks and would require advance public disclosure before selling them.

• Markwayne Mullin, who is mentioned in the lesson slides and video, was serving as a U.S. Senator from Oklahoma at the time this lesson was created. He has since left the Senate to become the U.S. Secretary of Homeland Security.
• An ideal market is fair (all investors have access to the same information) and efficient (prices adjust quickly as trades occur). In such a market, the probability of a stock gaining or losing value at any particular moment is about 50%. Why is this the case? Imagine a situation in which a stock has a much greater than 50% chance of increasing in value. Investors would recognize this opportunity and quickly begin buying the stock. As demand increases, the price would rise. This process would continue until the price reaches a level where the advantage disappears, bringing the probability of future gains back toward 50%. In this way, buying and selling activity continuously pushes prices toward a short-term equilibrium.
• Although the short-term probability of a stock increasing in value is about 50%, the long-term probability is somewhat higher. This is because the stock market as a whole tends to increase in value over time. The trades discussed in this lesson take place over a period of months, so we might expect the probability of a stock gaining value to be slightly above 50%. However, as shown in the lesson, Congressional representatives not only had more than a 50% chance of buying stocks that increased in value. They also had more than a 50% chance of selling stocks that decreased in value. Even in a setting where gains are somewhat more likely than losses, this combination of outcomes is notable.

• When combined with conditional probability, the addition rule can be used to derive the Law of Total Probability – a fundamental law in probability theory (outside the scope of this course). The Law of Total Probability enables the application of Bayes’ Theorem and Bayesian Statistics to a variety of probabilistic / statistical scenarios. Both Bayes’ Theorem and Bayesian Statistics are also outside the scope of this course. That said, as an enrichment activity, a high school-level exploration of these concepts can be found here.
• In the next unit, students will be introduced to binomial probability distributions, where independence is one of the key conditions that must be satisfied. The distinction between sampling with replacement and without replacement, and its connection to independence, is especially important in the binomial setting. This lesson lays the groundwork for that idea.
• Later in the course, independence will also become an important condition for statistical inference. In particular, students will revisit this idea when working with the 10% condition, which helps justify treating observations as effectively independent.