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Explain xkcd: It's 'cause you're dumb.
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Base Rate
Sure, you can talk about per-capita adjustment, but if you want to solve the problem, it's obvious that this is the group you need to focus on.
Title text: Sure, you can talk about per-capita adjustment, but if you want to solve the problem, it's obvious that this is the group you need to focus on.

Explanation

Ambox notice.png This explanation may be incomplete or incorrect: Created by a LEFTY. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.

The "base rate" is a type of base probability, which a statistical probability can be based on. The base rate fallacy is a type of error in which people are presented with the rate at which something occurs throughout an entire population along with more specific information information about a subset of that population, and tend to ignore the whole-population information in favor of the specific information. For instance, imagine a disease that is present in 1% of the population, for which there is a test with a 5% false-positive rate. This test might be presented as "95% accurate", and so people who receive a positive result from such a test are likely to think they have the disease. However, someone who receives a positive test result has only a 17% chance of actually having the disease; a much more likely reason for the positive result, occurring in 83% of all positive test results, is a false (wrong) positive.

In this case, the joke is that 90% of people are right-handed, so Cueball's claim that right-handers commit 90% of base-rate errors is itself a base-rate error. Further, the pointer is held in Cueball's right hand, indicating that he too is right handed as he makes the base rate error.

Something similar occurs in 1138: Heatmap, where Cueball makes inferences simply based on a population map of the US, instead of statistical evidence.

Transcript

Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.
[Cueball standing in front of a screen, holding a pointer. The screen shows a bar graph with 2 bars, labeled "L" and "R". The "R" bar is significantly greater than "L".]
Cueball: Remember, right-handed people commit 90% of all base rate errors.


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