Step by step
The question
Question: Is it a good sample?
To find how much people read, ask 30 people in the library.
1 Look at who was asked
They ask 30 people in the library.
30 people in the library
A good sample is like the whole group.
Everyone has the same chance to be picked.
good sample = like the whole group
2 See if they are all alike
They are all one kind of person.
Their answers will be alike, and the others get no chance.
= one kind of person → not like everyone
Careful!
Even many people from one group do not speak for everyone.
This sample is biased.
Careful: a big sample is not enough: it must be random
So no: the sample is biased.
= no: biased
3 Check
Let's check: could every person in the group be picked?
No.
Most of them could not.
So the answer is right!
most people could not be picked
Let's look back.
First: look at who was asked.
Then: see if they are all alike.
Last: check.
Answer
= no: biased