Data Dive · Rung 4 · What Isn't There · 4.1

These counties have clean air

A claim to test. It fails.

Runs in 25 minutes · everything you need is on this page · no network, no accounts, nothing for the students to open

4.1→ next · ← back · esc leaves0 / 4

The claim on the table

“These counties have clean air.”

Somebody drew the map, saw white, and wrote that sentence. Your job is to say whether the evidence carries it.

4.1 · These counties have clean air→ next · ← back · esc leaves1 / 4

The evidence

Median AQI by county -- with the blanks marked

Median air quality index by California county, 2024the twenty-two most populous counties - US EPA AirDatamedian AQIcountymedian AQI, measuredNO air monitor - blank, not clean43.5870Los AngelesSan DiegoOrangeRiversideSan BernardinoSanta ClaraAlamedaSacramentoContra CostaFresnoKernVenturaSan FranciscoSan JoaquinSan MateoStanislausSonomaTulareSolanoSanta BarbaraMontereyPlacer

Yellow bars are counties with no air monitor at all

6
of 58 counties have no monitor
261,239
people living in them
11,564
square miles

Napa. Yuba. Lassen. Modoc. Sierra. Alpine. Napa has more people than seven monitored counties.

4.1 · These counties have clean air→ next · ← back · esc leaves2 / 4

The verdict

White does not mean clean. It means nobody measured.

The blank one is not the safe one. It is the unmeasured one, and a recommendation that treats those as the same thing has already failed.

AskYou are siting a facility that affects air quality. One candidate county has a middling AQI; one is blank. Which is safer to build in?
The three questions
  1. Where does this data start and end, and who chose that?
  2. Does the evidence reach the claim?
  3. What would you need before you would sign it?
4.1 · These counties have clean air→ next · ← back · esc leaves3 / 4

After the dive

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

the choropleth map

Which areas have more of this. Colour intensity by region.

What it leaves outBig areas shout. A large empty region looks more important than a small crowded one.
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

4.1→ next · ← back · esc leaves4 / 4