150 adults were chosen at random from a town. Half of them chose to…

Step by step

The question

Question: 150 adults were chosen at random from a town.

Half of them chose to walk every morning.

The walking group felt less tired.

What can the study say?

1 Two questions

To judge a study, we ask two questions.

How were the adults picked?

And how were the groups made?

2 How they were picked

The story says the adults were chosen at random from the town.

So: yes.

At random means all the adults in the town had the same chance to be picked.

So the group is a fair small copy of the whole town.

So what we find can be used for the whole town: true for all adults in the town.

3 How the groups were made

The adults chose for themselves.

So: no, not at random.

People who choose to walk every morning may be different in other ways too.

Careful!

Doing better does not prove the walking caused it.

Something else may make the difference.

So the walking and the better result go together.

But maybe the walking did not cause it.

4 What the study can say

So the study can say: in the town, the walking and the result go together, but maybe the walking is not the cause.

5 Check

Let's check with the story.

The first sentence says: chosen at random from the town.

That matches.

The second sentence says: they chose.

That matches too.

So the answer is right!

Let's look back.

First: two questions.

Then: how they were picked.

Then: how the groups were made.

Then: what the study can say.

Last: check.