representative sample

When you can not (or do not want) to count/survey everyone/thing in the population you use a SAMPLE.

Which best describes a sample?

• A sample is a complete count of every individual in the population.
• A sample is a subset of individuals chosen from a larger set.

The sample should REPRESENT the population so you can INFER what the larger group is like.

If you take a BAD sample, it does not allow you to make inferences about the larger population.

Choose the option below that says "Biased Sample"

• A sample that accurately represents the population
• A sample that is selected randomly from the population
• Biased Sample

Key vocab word: Representative Sample

The sample represents the population.

Choose the answer that says "Representative Sample"

• Random Sample
• Biased Sample
• Representative Sample

Look at our population, 20% of the dots are red.

A representative sample would ALSO have 20% red dots.

Draw what a representative sample would look like.

There are 15 circles in the population.

If I take a RANDOM sample of 3 circles, which are possible outcomes?

Which of the following are possible RANDOM samples?

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Answer explanation

THEY ALL ARE!

If I randomly choose 3 dots it could be ANY 3 dots.

They are all possible!

There are 15 circles in the population.

20% of the circles are red.

The best representative sample would also have 20% red circles.

It is RARE for your sample to be EXACTLY the same. We hope the sample is SIMILAR or CLOSE.

In a sample of 3 each circle is 33% (so not 20%). Which sample is the MOST representative of the population?

Which is the BEST sample of the 4 random samples?

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Answer explanation

The population is MOSTLY purple and SOME red.

This is the only sample that is MOSTLY purple and some red.

This is the MOST representative sample even though it is not exactly the same as the population.

If the population is ALL 7th Graders

Then you want to take a sample from ALL 7th graders.

A sample is part of the population but not all of it.

Select the one below that is true

• A sample is a smaller group selected from the population
• A sample is the entire population
• A sample is a larger group than the population
• A representative sample is not related to the population

Another word for a "smaller group"

is

SUBSET

Your sample is a subset of the population.

Which answer describes a sample?

• A sample is a SUBSET selected from the population

• A sample is the entire population
• A sample is a larger group than the population

BEWARE: Your sample does not allow for someone in China to be represented.

If you survey students in your town then your population is limited to students in your town.

What makes a sample representative?

• The sample is representative if it includes people from all over the world
• The sample is representative if it includes people from the same town
• The sample is representative if it includes people from the same country
• The sample is representative if it accurately reflects the group it is supposed to represent

When taking a sample

You want to choose individuals/objects

FROM THE POPULATION

Anyone in the population could potentially be part of the sample is ideal.

Which below is the best way to take a sample?

• Only select individuals who are easily accessible
• Select individuals based on personal bias
• Select individuals randomly from the entire population
• Only select individuals who respond to a public survey