200 people were chosen at random from a city. Half of them were… Step by Step

Step by step

The question

Question: 200 people were chosen at random from a city.

Half of them were chosen at random to drink green tea each day.

The tea group slept longer.

What can the study say?

1 Two questions

To judge a study, we ask two questions.

How were the people picked?

And how were the groups made?

2 How they were picked

The story says the people were chosen at random from the city.

So: yes.

At random means all the people in the city had the same chance to be picked.

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

random: all people in the city had the same chance

So what we find can be used for the whole city: true for all people in the city.

3 How the groups were made

The people were chosen at random to drink green tea each day.

So: yes.

Chance made the groups, not the people.

So the two groups are alike, except for the tea.

random groups: alike, except for the tea

So the difference comes from the tea: the tea causes it.

Careful!

Only for the city they were picked from.

Not for all people everywhere.

Careful: not true for all people everywhere ✗

4 What the study can say

So the study can say: for all people in the city, the tea causes this.

= causes it, for the whole city

5 Check

Let's check with the story.

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

That matches.

"chosen at random from" → all the city

The second sentence says: chosen at random to drink green tea each day.

That matches too.

So the answer is right!

"chosen at random to" → causes

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.

Answer