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Can the place with more accidents be safer per visit?

Ten accidents sound worse than two, until you learn how many visits each place receives. In an imaginary comparison, 10 accidents in 100,000 visits is a lower rate than two in 1,000. The comparison still depends on what counts as an accident, how long visits last, and how serious the outcomes are.

3–5 min

Questions you could explore

  • When would time spent at a place be a more useful denominator than visits?

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Maths and statistics

When one long wait changes the average

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5–7 min

When one long wait changes the average

Maths and statistics5–7 minAn average wait can sound straightforward until one person waits much longer than everyone else. The mean and median offer two ways to summarize that same group. Their different responses to an unusually large value raise a practical question: what do we want an average to tell us?

Maths and statistics

How is random sampling different from random assignment?

A study can choose people at random, assign them to groups at random, do both, or do neither. Those choices answer different problems: who the findings may describe, and how fairly the study compares conditions.

3–5 min

How is random sampling different from random assignment?

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Why does the Gregorian calendar sometimes skip a leap year?

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