# Chapter Three

# Beware the Base Rate

Does the sign above tell you whether you are more likely to drown if you are not wearing a life jacket? Think about it a bit. Derek Bruff, the mathematician who took this picture, points out the sign doesn’t tell you anything unless you know what percentage of people wear lifejackets on the lake. Imagine [...]

# Accounting for Randomness (Part I: Perils of a Small Sample)

Thinking about Randomness Randomness (and probability) is one of the more difficult things to understand. In this course we do not go into nearly the detail that most statistics courses go into on randomness. Instead, we are going to try to get across a few main points. The point we want to get across here [...]

# Weighted Means & Standardization

You probably already know about and have used weighted means — they are one of the most popular ways for professors to calculate grades. For example, if quizzes are going to be 30% of the grade and the midterm + final is going to be 70% of the grade then if your grades look [...]

# Controlling for Populations with Percentages and Per Capita

One of the most common comparison controls we use is controlling for population, both when looking at something societal (percentage of people out of work) and at experimental results (percentage of people experiencing a positive outcome). Percentages and Natural Frequencies Take for example this list of the top 15 countries in terms of number of [...]

# Activity Questions Following “Controlling for Populations with Percentages and Per Capita”

1. Notice the difference between the number of prisoners indicated in the NationMaster data, and the number of prisoners indicated by the BJS statistics. Read the definition on the BJS statistics carefully, and then come up with a definition that explains why the NationMaster stats are higher.

# Activity: 24 Houses Per Homeless Person

Via Truth & Justice’s Facebook Page. Find a figure (or a couple of figures) on homelessness in America. Find a figure on the number of houses in America. What percentage of houses would have to be unoccupied for this to be true? Does it sound plausible? Do a mental experiment — if we reduced homelessness [...]