1. Questions for thought
If you think your school is the best school in the world, raise your hand.
What’s the problem with this survey?
To see what percentage of Canadians like curry, a survey is conducted in Toronto.
What’s wrong with this survey?
How could you make these surveys better?
In groups of your choosing, brainstorm four ways to survey student’s favourite tv shows within the school.

2. Unit 3 – One Variable Statistics
SAMPLING TECHNIQUES
Unit 3 – One Variable Statistics

3. Statistics
The study of the collection, organization, analysis, interpretation, and presentation of data.

4. Key terms
Population – all individuals or items that belong to a group being studied.
Sample – The group of people chosen for a survey.
Census – A survey where the sample is the whole population.
Bias Results – Misleading or not representative of the whole population.

5. Sampling Techniques Simple Random Stratified Random Systematic Cluster
Convenience
Voluntary response

6. 1. Simple Random Sample
Each member of the population has an equal chance of being selected.
Example: Drawing 5 names from a hat of a total of 30 names.
Pros
Cons
Easy to do
Fair to all involved
Could get poor representation (i.e. all people chosen have same opinion)

7. 2.Stratified Random Sample
Population is divided into subgroups (i.e. gender, age, nationality) and then a random sample is taken from each subgroup. Example: Dividing a school by grades and randomly selecting from each grade.
Pros
Cons
Fair representation of the population
Increased setup time
Could still be biased
Survey may not be relevant to certain subgroups

8. 3.Systematic Sample Choosing every nth member of the population
Example: A light bulb manufacture r tests every 100th light bulb
Pros
Cons
Easy to do
Spreads sample evenly over population
Could be hidden pattern in the system

9.
Clip on Simple, Systematic, and Stratified Sampling

10. 4.Cluster Sample
Population is divided into clusters and a random number of clusters (or cluster) is chosen as a sample
Example – Clusters could be the set of students sitting at a table. Not necessarily a specific grouping.
Pros
Cons
Easy to do
Often over-represents some opinions as clusters have a higher chance of sharing opinions

11. 4.Convenience Sample
Sample composed of those that it is easiest to get data from.
Example: Sampling friends, conducting internet or telephone survey.
Pros
Cons
Easiest to do
Good way to start research and get ideas
Not randomized
High chance that sample doesn’t represent population

12. 4.Voluntary-Response Sample
Sample contains population members who volunteer to do the survey
Example: Those with pet allergies may volunteer to do a study on their allergies
Pros
Cons
Often useful for psychological and/or pharmaceutical trials
Participants sometimes vote more than once and skew change) the results