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3.4
Sampling
P
urpose
The role this topic plays in quantitative reasoning
How does the Gallup Poll report the expected voting behavior of a state’s population without asking the
entire population? Your smart phone company has just received a shipment of 5,000 batteries. How does
your company ensure the quality of the shipment without testing all the batteries?
There are many situations where you would like to know the characteristics of an entire population,
i.e., a large group of people or objects, but it is impossible or impractical to survey every individual
in the whole population. Instead a sample of the population is collected, surveyed or tested and these
results are analyzed to gain an understanding of the behavior of the entire population. For example,
a production line might test a sample of products to determine quality, a campaign committee might
sample potential voters to determine how their candidate is faring, a drug company may test a sample to
see the side effects of their product, or a market research company might survey a sample to determine
the favorability of the new feature of a product. Almost daily, you will see the results of such sampling
in advertisements, political statements, and in the products available to you.
Choosing the appropriate sampling strategy is a key to successful research study. Without reliable sample
data, inferences that are made from the sample may biased. In this activity you will review sampling
strategies that are used to obtain data, the sample sizes that are necessary to ensure proper inferences,
and the possible costs to obtaining the data.
L
earning Goals
What you should learn while completing this activity
1. Use appropriate sampling techniques and strategies for a given situation.
2. Determine the sample size considering importance of the situation, value the data can produce,
margin of error needed and cost to collect.
3. Identify quality issues in sampling such as bias, non-probability samples, or non-compliance.
D
iscovery
Finding out for yourself
Make a list of five things you know or think you know about how the Nielsen Ratings work. Then read
the short article on the Neilsen Ratings available on the companion website. Now examine the list you
wrote and determine which items were true and why; which were untrue and why? How important are
the Neilsen Ratings in determining which shows and advertisements are made available? How much do
you think it costs to determine the ratings each year?
W
hat Do You Already Know?
Tapping into your existing knowledge
1. What sampling techniques have you used or experienced before?
2. What are reasons that sampling is used?
3. What sampling methods are you aware of?