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A made-up fire service records six fires: the number of fire engines sent and the repair cost…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A made-up fire service records six fires: the number of fire engines sent and the repair cost afterwards, in thousands of euros. The engines are , , , , and , and the costs are , , , , and . Find to four decimal places. Do more fire engines cause more damage? Name the lurking variable.
Need a reminder? The key ideaShow
A lurking (confounding) variable affects both variables and can create a correlation. A correlation can also come from reverse cause, mixed groups, time or chance. Only a randomised experiment balances lurking variables that nobody knows about.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. r. engines and thousand euros. The sums give .
Step 2. Cause? No. A bigger fire makes the service send more engines, and a bigger fire also does more damage.
Answer: ; the lurking variable is the size of the fire.
What if? To learn whether more engines reduce damage, compare fires of the same size. Within fires of one size, more engines would probably mean less damage.
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