Data Dive · Rung 3 · What's Related · 3.2

A mean is a deletion

Shown with something they already know was deleted.

Runs in 20 minutes · everything you need is on this page · no network, no accounts, nothing for the students to open

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The summary

Average 311 requests, by month

Mean 311 requests per day, by monthLos Angeles, 2022 - an average is a machine for removing outliersmean requests per daymonth of 2022monthly meanSeptember - it contains a day of 952,0134,02504,002013,563023,745033,473043,532053,931063,772074,025083,620093,565103,248113,16412

Los Angeles, 2022. September marked.

7th of 12
September's rank
3,620
its mean -- the middle of the pack
AskWhich month was strangest in 2022?
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What it removed

September contains a day with 95 requests

Against a month whose maximum is 5,754. That 95 is the twenty-two-hour outage. A whole session's finding, invisible here.

Not because anyone lied. An average is a machine for removing exactly that.

The three questions
  1. What has this chart thrown away to make itself readable?
  2. Which month looks strangest here, and which actually was?
  3. You know what was deleted because you found it. What else has been averaged away from you?
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After the dive

The shapes on this page, in the library’s own words

the bar

Bar length is the value, so it only means anything measured from zero. Start the axis anywhere else and the lengths stop matching the numbers.

What it leaves outOrder is a choice. Sorted by size it is a ranking; sorted by name it is a lookup; and the same bars say different things in each.
the box plot

The middle half of the data sits in the box. It shows the spread, not how many.

What it leaves outThe box hides how many. Five values and five hundred draw the same box, and a gap in the middle of the data does not show at all.

library · ladder · dives · the pool · this dive’s worksheet

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