Data Dive · Rung 1 · What's There · 1.3

A number with no comparison

Two stages, and the order is the lesson.

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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Stage one — alone on the screen

Los Angeles County, 2024

78
days unhealthy for sensitive groups

Every student will answer. None of them can. Sit in it for a moment before you move on.

AskIs that a lot?
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Stage two — the same file, everyone else

All 58 California counties

Days unhealthy for sensitive groups, 2024the worst fourteen California counties - US EPA AirDataunhealthy days in 2024countyanother California countyLos Angeles County - third, not first41.583083Tulare80Riverside78Los Angeles73Kern65Fresno56San Bernardi48San Diego42Imperial38Stanislaus34Merced33Kings27Placer25Madera17Inyo

Unhealthy-air days, 2024. Los Angeles marked.

3rd
of 52 measured counties
80
Riverside, worse than LA
0
Santa Cruz, Siskiyou, Sonoma

Against zero, 78 is enormous. Against Riverside, it is ordinary. And Los Angeles is not the worst. Ask whether they expected that.

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The point

A number alone is not a finding

It is half of one. The other half is what you compare it to, and whoever picks the comparison has already done most of your thinking for you.

The three questions
  1. What kind of chart is a single number, and what is it hiding?
  2. Is 78 a lot? Answer twice -- before and after.
  3. You breathe this air. Which comparison would you want used when somebody decides whether to act?
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After the dive

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

the number

One value, on its own. It is not a trend and not a spread — just the one number.

What it leaves outA number with nothing beside it cannot be big or small. 46.5% of what, measured when, compared with which other year?
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.

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

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