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A news story says that a habit raises the risk of a certain illness by 25%…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A news story says that a habit raises the risk of a certain illness by 25%. Without the habit, 4 people in every 1000 get the illness in a year. How many people in every 1000 get it with the habit? In a city of people who all had the habit, how many extra cases would there be in a year?
Need a reminder? The key ideaShow
A confounding variable is linked to both the explanatory and the response variable. Compare like with like inside groups, or assign at random. A relative rise of on a risk of per 1000 adds people per 1000.
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. The new risk. people in every 1000.
Step 2. The extra cases. One extra case in every 1000 people. The city has thousands, so there are extra cases.
Answer: 5 in 1000, and about 200 extra cases a year.
Check. The relative rise sounds large, but the absolute rise is 1 person in 1000. Both are true, and both help a city plan.
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