# Biased Samples

In this worksheet, students must state whether a sample is biased.

Key stage:  KS 4

Curriculum topic:  Probability

Curriculum subtopic:  Use a Probability Model to Predict the Outcomes

Difficulty level:

### QUESTION 1 of 10

When a sample is biased, some people or items are more likely to be chosen than others.

Example 1

A group of 35 school children are surveyed. Is the sample likely to be biased?

Yes, because they may have different opinions to others in the school.

Example 2

Jack selected 15 cards randomly from a pack of cards. Is the sample likely to be biased?

No, because the cards were randomly chosen and there is an equal chance that each card will be chosen.

A group of 35 workers from a factory are surveyed.

Is the sample likely to be biased?

yes

no

Sam surveyed his two Sports teachers at school.

Is the sample likely to be biased?

yes

no

A head teacher surveyed a random group of 20 children in assembly.

Is the sample likely to be biased?

yes

no

Ann poured a packet of sweets into a bowl. The sweets were all the same size and shape but differently coloured. She shook the bowl and poured 10 sweets on to the table.

Is the sample likely to be biased?

yes

no

Mr. Brown chose the children who came in the top ten positions in an English exam to survey them about a new novel.

Is the sample likely to be biased?

yes

no

Mrs. Smith chose two children randomly from each class to survey them about a new novel.

Is the sample likely to be biased?

yes

no

Ahmed has a jar full of 10p coins.

Without looking, he takes 20 coins from the jar.

Is the sample likely to be biased?

yes

no

Ahmed has a jar full of 10p coins.

He takes out the ten cleanest coins.

Is the sample likely to be biased?

yes

no

Sumi chooses three different brands of pasta as a sample to analyse the ingredients in pasta.

Is the sample likely to be biased?

yes

no

Tony randomly chooses five floor tiles from three boxes of floor tiles.

Is the sample likely to be biased?

yes

no

• Question 1

A group of 35 workers from a factory are surveyed.

Is the sample likely to be biased?

yes
EDDIE SAYS
They may have different opinions to other workers.
• Question 2

Sam surveyed his two Sports teachers at school.

Is the sample likely to be biased?

yes
EDDIE SAYS
They may have different opinions to other teachers.
• Question 3

A head teacher surveyed a random group of 20 children in assembly.

Is the sample likely to be biased?

no
EDDIE SAYS
This is a random sample.
• Question 4

Ann poured a packet of sweets into a bowl. The sweets were all the same size and shape but differently coloured. She shook the bowl and poured 10 sweets on to the table.

Is the sample likely to be biased?

no
EDDIE SAYS
This is a random sample.
• Question 5

Mr. Brown chose the children who came in the top ten positions in an English exam to survey them about a new novel.

Is the sample likely to be biased?

yes
EDDIE SAYS
Those who were not in the top ten may have different opinions.
• Question 6

Mrs. Smith chose two children randomly from each class to survey them about a new novel.

Is the sample likely to be biased?

no
EDDIE SAYS
The children are randomly selected.
• Question 7

Ahmed has a jar full of 10p coins.

Without looking, he takes 20 coins from the jar.

Is the sample likely to be biased?

no
EDDIE SAYS
The coins are randomly selected.
• Question 8

Ahmed has a jar full of 10p coins.

He takes out the ten cleanest coins.

Is the sample likely to be biased?

yes
EDDIE SAYS
The coins are not randomly selected and he may have selected the newest coins.
• Question 9

Sumi chooses three different brands of pasta as a sample to analyse the ingredients in pasta.

Is the sample likely to be biased?

yes
EDDIE SAYS
There may be other completely different brands using different ingredients.
• Question 10

Tony randomly chooses five floor tiles from three boxes of floor tiles.

Is the sample likely to be biased?

no
EDDIE SAYS
The five selected tiles have been randomly chosen and so represent all the tiles.
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