Data Dive 1.3

Is 78 bad-air days a lot?

A number means nothing until you compare it to something.

You will need paper and a pencil, and a browser for step 3

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Step 1 of 5 · Your guess

What do you think?

Your cousin's family lives in Los Angeles County. Her mom read that in 2024, LA had 78 days when the air was unhealthy for sensitive groups: kids, older people, and anyone with asthma.

She says the family should move.

Write it down before you lookIs 78 a lot? Write yes, no, or can't tell, and one reason.
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Step 2 of 5 · Look

The worst air in California

Bad-air days in 2024, the fourteen worst California countiesdays the air was unhealthy for sensitive groups - US EPA AirDatabad-air days in 2024countyanother California countyLos Angeles County41.583083Tulare80Riverside78Los Angeles73Kern65Fresno56San Bernardino48San Diego42Imperial38Stanislaus34Merced33Kings27Placer25Madera17Inyo

Bad-air days in 2024 for the fourteen worst of the 52 California counties that measure their air. Los Angeles is marked.

How to read it. Each bar is one California county. The longer the bar, the more days that year the air was unhealthy for sensitive groups.

Find out
  1. Find Los Angeles. Is it the worst?
  2. Now that you can compare, has your answer about 78 changed?
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Step 3 of 5 · Try it

Now you try it, on the same data

This opens the pool, the site's chart tool. The words in bold below are buttons and menus you will see on the screen.

Do these five things

Open the pool on this file: data.sfhsbta.com/thepool?file=number_la_aqi_california_counties.csv&mark=bar

  1. Under across, pick county. Under up, pick unhealthy_sensitive_days. Set order to by value. Where does Los Angeles rank?
  2. Count the counties that had zero bad-air days.
  3. Set top to 5. Which counties are worse than Los Angeles?
  4. Set top back to all. Set keep from to 50 and keep to to 100. How many counties are left? These are LA's neighbors on the chart.
  5. Pick a county you would tell the family to move to. What did you compare it to?
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Step 4 of 5 · Say it

Your answer, in one sentence

I think 78 bad-air days is <a lot or not a lot> because <what the chart shows> and I checked it by <what you did to the chart>.

The last part matters most. It shows you did not just look at the chart, you tested it.

Here is one exampleI think 78 bad-air days is a lot for California, because 15 counties had zero, but LA is not the worst, because Tulare had 83. I checked by setting top to 5.
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Step 5 of 5 · What you found

Check your numbers

3rd of 52
LA's rank among the counties with an air monitor
15
counties with zero bad-air days
6
counties between 50 and 100 days, LA included
The big idea: contextA number by itself is only half a finding. The other half is what you compare it to. Compared with zero, 78 is terrible. Compared with the worst counties, it is ordinary. Whoever picks the comparison is shaping your answer.
One more thing to think aboutSix California counties have no air monitor, so they are not in this file at all. What does this chart tell you about their air?
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After the dive

The charts you used today

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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