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A made-up survey asks 200 people whether they own a dog and whether they live in a flat…
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 survey asks people whether they own a dog and whether they live in a flat. own a dog and live in a flat. Fill in the four counts of the table so that owning a dog and living in a flat are independent. Give the count of dog owners in flats, dog owners in houses, people without a dog in flats and people without a dog in houses.
Need a reminder? The key ideaShow
Two answers are independent when the share of one is the same in every group of the other, so . Then each expected count is the row total times the column total, divided by the grand total.
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. Dog and flat. people.
Step 2. The rest of the dog row. dog owners in houses.
Step 3. The rest of the flat column. people without a dog in flats.
Step 4. The last cell. people.
Answer: , , and people.
Check. The share of dog owners is in flats and in houses, the same as overall.
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