Population and Sample Lesson

Population, Sample and Bias Lesson

Population Vs. Sample

Let's look at an example...

Parent council wants to know how students feel about the options of special lunch days at your school. They surveyed a random sample of 100 students from the school to see if they should offer new options!

Multiple Choice

The sample is...

• all of the students in the school

• the 100 students randomly surveyed

• all of the people in the school (including adults)

• all of the people in the city of Hamilton

Multiple Choice

The population is...

• the 100 students surveyed

• all of the people in the city of Hamilton

• all students attending elementary school in the HWDSB

• all of the students attending your school

Definitions...

Population: the total set of subjects (eg. individuals, objects, species) that fit a particular description; in our example, all of the students at your school would be the population.

CENSUS Survey: Data collected by surveying the entire population.

In our example the if EVERYONE at your school was surveyed, that would be a census survey.

Census survey's can be expensive and time -consuming for large populations.

Definitions...

Sample Survey: gathering information from a subset of a population (known as a sample). In our example the 100 people surveyed would be the sample. It's not efficient to survey EVERYONE at your school, so we survey a random group that will represent the population.

Secondary Date: Date that is not collected by yourself.

Sample surveys are less costly and require less time.

The results may not be accurate because not everyone has input.

Avoiding Bias

A sample is BIASED if it does not accurately represent the population.

A sample is RELIABLE if the results can be duplicated in another survey.

A sample is VALID if the results represent a population.

It's important that you carefully consider how you choose your sample to avoid bias! Here are some sampling methods that help give you the most accurate results. Selecting a sample is important - you don't want to waste time surveying people that won't represent the population you are interested in!

Examples of Sampling Methods

• Simple Random Sample - each person has an equal chance of being selected - you might use software to help you choose a random sample (computers are unbiased)

• Stratified Random Sampling - you divide your population into groups (age is often used) and select random people from each group

Primary Data

Data collected by Yourself.

Multiple Choice

A sample in which every person, object, or event has an equal chance of being selected.

• biased sample

• unbiased sample

Multiple Choice

When a sample does not accurately represent the population it is a:

• biased sample

• unbiased sample

Multiple Choice

Ana wants to know the average student’s opinion of the late policy at her school. Which group of students should she survey in order to achieve the most accurate results?

• 30 students that are always late for school

• all of her friends

• 30 random students from her school

• the parents on Parent Council

Multiple Choice

At a middle school, the 7th graders will conduct a survey for where to go on a field trip.

Which method will result in the least biased decision?

• To randomly ask 8th grade students who went on a field trip last year.

• To randomly choose some 7th grade students to select a location.

Multiple Choice

Larger random sample sizes are more representative of a population.

• True

• False

Multiple Choice

To find out if the school cafeteria should change its menu, all the teachers were surveyed.

• Biased

• Unbiased

Multiple Choice

Hockey magazine asks its readers to reply to a question about the favorite sports of teenagers.

• Biased

• Unbiased

Multiple Choice

The owners of the City Mall want to find out if shoppers would like a video arcade to be opened in the mall. How might the

survey results be affected in each situation?

• A survey of all shoppers is taken on a weekday morning.

• A survey of all shoppers taken is taken on a Saturday afternoon.

• A survey of teenage shoppers is taken.