Data Dive · Rung 2 · What's Reported · 2.2

Two instruments that are not independent

The obvious way to check a proxy, and why it does not work.

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The obvious move

Complaints are only a proxy -- so go and check

New York inspects properties and records what it finds. Real inspectors, real rats. That should settle it.

It does not, and finding out why is the whole dive.

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The tell

Inspections dispatched per complaint

Inspections dispatched per complaint, 2024if the two measurements were independent this would be flatinspections per complaintboroughinspections per complaint4806.1Brooklyn7.5Manhattan2.3Queens8Bronx1.4Staten Island

2024. If the two measurements were independent, this would be flat.

1.4
Staten Island
8.0
the Bronx
r = 0.907
how tightly they track

The city inspects because somebody complained. So the second measurement was caused by the first.

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The sentence

You cannot check a proxy with a measurement the proxy triggered

That ratio is not a fact about rats. It is a fact about how a city answers a phone call.

And the ranking still moves: the Bronx is fourth in complaints and third in confirmed rat activity. The proxy gets the order wrong.

The three questions
  1. What was actually measured, and what caused the measuring to happen?
  2. Rank the boroughs by complaints, then by confirmed activity. What moved?
  3. If your block has rats and nobody on it calls, what happens to your block in every chart here?
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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.

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