# Lurking Variable USEans

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Lurking Variables
For each of the scenarios described below, list at least one possible lurking variable.
1.
FIRE DAMAGE AND FIRE TRUCKS
The amount of damage at the scene of a fire has a positive correlation with the number of fire trucks on the scene.
The extent of the fire is a lurking variable. We can relate this numerically to the number of alarms – a three-alarm,
four-alarm, or five-alarm fire. The bigger the fire, the more fire trucks are called in. At the same time, the damage
from the fire is more extensive.
2.
BUNDLED-UP BABIES AND OUTDOOR TEMPERATURE
The age at which a baby first learns to crawl has a negative correlation with outdoor temperature.
The higher the outdoor temperature, the younger the age at which babies learn to crawl. (Or, the lower the
temperature, the older the age that babies learn to crawl.)
Possible lurking variables:


3.
the amount of clothing babies wear in the winter time (thus their movement is restricted)
the amount of outdoor time babies get
DANGEROUS ICE CREAM AND DROWNINGS
The number of ice cream servings consumed has a positive correlation with the number of drownings.
(Hint: What else is going on when people swim?)
Outdoor temperature is a possible lurking variable
4.
CAR COST AND GAS MILEAGE
In 2005, there was a negative correlation between car cost and gas mileage.
Lurking variables: Engine size and car weight. The more expensive cars tend to have larger engines, which get
fewer miles per gallon. Also, the more expensive cars tend to be larger and, on average, less fuel efficient.
Note: Hybrid cars can be outliers here.
5.
Foot size and reading ability have a positive correlation.
Child’s age is the lurking variable.
Reference
MATHEMATICS TEACHER|Vol. 106, No. 6. February 2013
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