Chapter Five

Base Rate Refresher

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You Meet a Guy Named John Base rates are extremely important, but we neglect them all the time. In fact, we do worse than that, because we exaggerate the importance of data apart from base rates. In an article about the statistics of predicting marriage success, reporter Laurie Abraham gives a classic example of how we ignore [...]

Guesstimating: How to Sanity Check Any Figure

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As part of our focus on doing mental experiments, we want to introduce you to the wonderful world of guesstimating. While guesstimating — the ability to guess at what a statistic might be using only information available to you — is seen by some as a trivial magic trick, in reality it is an extremely [...]

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Graphing Longitudinal Comparisons

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How has student borrowing for education changed over time? Here’s one look at that question, shown as a bar chart: Visually the impact is striking — but as with all comparisons we need to make sure we actually understand the terms of the comparison. First, you need to ask what is being measured. When longitudinal [...]

Top and Bottom Quintile

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In the COMPARABLE framework, the “Question of Edges” is a placeholder to remind us that measures of central tendency such as mean, median, and mode are helpful, but only tell us so much. One way to get a sense of the distribution of values is to use quintiles. With quintiles, we start out by imagining [...]

Predicting with Percentages (Review)

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Quick review of our idea of “representativeness”: When we hear a percentage (For example, 41% of college students are male vs. 59% female) used to advance a theory (fewer men want to go to college) we can make predictions based on assumptions (if the reason for the non-representation is lack of applicants then SAT participation [...]

Touchstone Figures: Population

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 (BEWARE! FOR GUESSTIMATION ONLY! BRUTALLY ROUNDED!) 20 billion: Number of chickens in world 7 billion: Population of World (humans) 4 billion: Population of Asia (2010) 3 billion: Population of the World, 1960 1 billion: Population of China, Population of the world in 1800, Population of Africa, number of cattle in world (2010) 600 million: Population of Europe [...]