90 cows were chosen at random from a farm. Half of them were picked… Step by Step

Step by step

The question

Question: 90 cows were chosen at random from a farm.

Half of them were picked at random to eat a new grass.

The grass group gave more milk.

What can the study say?

1 Two questions

To judge a study, we ask two questions.

How were the cows picked?

And how were the groups made?

2 How they were picked

The story says the cows were chosen at random from the farm.

So: yes.

At random means all the cows in the farm had the same chance to be picked.

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

random: all cows in the farm had the same chance

So what we find can be used for the whole farm: true for all cows in the farm.

3 How the groups were made

The cows were chosen at random to eat a new grass.

So: yes.

Chance made the groups, not the cows.

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

random groups: alike, except for the grass

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

Careful!

Only for the farm they were picked from.

Not for all cows everywhere.

Careful: not true for all cows everywhere ✗

4 What the study can say

So the study can say: for all cows in the farm, the grass causes this.

= causes it, for the whole farm

5 Check

Let's check with the story.

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

That matches.

"chosen at random from" → all the farm

The second sentence says: chosen at random to eat a new grass.

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