Chapter Outline

5.1 Populations and Samples

5.2 The Power of Random Sampling

Random Samples

Sampling Evidence in the Courtroom

Choosing a Random Sample

Random Number Generators

5.3 A Study of the Break-Even Effect

Imprecise Populations

Texas Hold ’Em

5.4 Biased Samples

Selection Bias

Survivor Bias

Does Anger Trigger Heart Attacks?

5.5 Observational Data versus Experimental Data

Conquering Cholera

Confounding Factors


“Data! data! data!” he cried impatiently, “I can’t make bricks without clay.”

Sherlock Holmes

We use probabilities to describe how likely it is that something will happen. Data, in contrast, are a record of things that actually have happened. Here are three examples:

A fairly flipped coin

Probability: ...

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