1. Probability & Statistics
Sampling Techniques

2. Sampling Techniques 13.1 Sampling Techniques
T. Serino
13.1 Sampling Techniques
Population: All items or people of interest.
Sample: Some items of a population.

3. Sampling Techniques
T. Serino
Statisticians often use a sample in order to make predictions about a whole population.
When a statistician draws a conclusion from a sample, there is always the possibility that the conclusion is incorrect.

4. Sampling Techniques Why use a sample instead of a population?
T. Serino
Why use a sample instead of a population?
1.  It is often impossible to obtain data on an entire population.
2.  Sampling is less expensive because collecting data takes less time and effort.
More simply put…
Studying samples saves and
Time ,
money
Effort

5. Sampling Techniques
T. Serino
In this unit, we will study some sampling techniques that attempt to collect unbiased samples of different populations.
An unbiased sample is a small replica of the entire population.
Definition:
Unbiased:  1. having no bias or prejudice; fair or impartial   statistics (of a sample) not affected by any extraneous factors, conflated variables, or selectivity which influence its distribution; random

6. Sampling Techniques
T. Serino
If care isn't taken while collecting data or selecting a sample of the population, results could be biased.
Definition:
Bias:  a particular tendency or inclination, especially one that prevents unprejudiced consideration of a question; prejudice.

7. Sampling Techniques Random Sampling
T. Serino
Sampling Techniques
Random Sampling
A sample drawn so that each item in the population has an equal chance of being selected.
For example, a jar contains 200 marbles that are identical except for color. Half of the marbles are red and the other half of the marbles are blue. A random sample can be easily achieved by selecting marbles from the jar (without looking).

8. Sampling Techniques Systematic Sampling
T. Serino
Systematic Sampling
A sample obtained by drawing every nth item on a list or production line. (The first item should be determined by using a random number.)
For example, to determine how often damaged items are produced, every tenth item is checked for damage.
(In this example, n = 10.)

9. Sampling Techniques Cluster Sampling (or Area Sample)
T. Serino
Cluster Sampling (or Area Sample)
A random selection of groups or units. (Groups are often geographic locations.)
For example, to estimate the average income of the residents of Lynn, a random sample of 100 residents was taken from each zip code in the city.

10. Sampling Techniques Stratified Sampling
T. Serino
Stratified Sampling
Dividing the population by characteristics that can usually be ordered by level. (Income, career, and social status are typical stratified characteristics, but gender, race, or religion can also be considered stratified.)
For example, upper income, middle income, and lower income families were sampled to determine the average number of children per household.

11. Sampling Techniques Convenience Sampling
T. Serino
Convenience Sampling
Data that is easily or readily obtained.
(Warning: This type of sampling can be extremely biased)
For example, a teacher was interested in predicting who would become the senior prom queen. His period two class consisted of all seniors. He surveyed the period two class to see who they would vote for at the prom.

12. Sampling Techniques Review: 5 Sampling Techniques
T. Serino
Review: 5 Sampling Techniques
Random Sampling: Blindly choosing from a whole population
Systematic Sampling: Choosing every nth item
Cluster Sampling: Taking a sample from different Areas or groups
Stratified Sampling: Taking samples from different levels
Convenience Sampling: Sampling whatever is easy

13. Sampling Techniques Try this.
T. Serino
Try this.
Identify the sampling technique described.
a. A raffle ticket is drawn by a blindfolded person at a festival to win a grand prize.
b. Students at an elementary school are classified according to their present grade level. Then, a random sample of three students from each grade is chosen to represent their class.
c. Every sixth car on highway is stopped for a vehicle inspection.

14. Sampling Techniques Try this.
T. Serino
Try this.
d. Voters are classified based on their polling location. A random sample of four polling locations is selected. All the voters from the precinct are included in the sample.
e. The first 20 people entering a water park are asked if they are wearing sunscreen.

15. athematical M D
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