The Logic of Sampling
Key Sampling Concepts
•
•
•
•
•
•
Sampling (two types)
Element
Population
Sample
Sampling Frame
Representative Sample
Application of Sampling Terms
Types of Samples
• Probability -- Strictly following two rules.
• Non Probability -- Failing to follow the two
rules
Types of Probability Samples
•
•
•
•
Simple Random Sample (SRS)
Systematic Random Sample
Stratified Random Sample
Cluster Sample
Simple Random Sample
• Every element has an equal chance of
selection
• No element can be selected more than once
Example of a good random sample outcome
Simple Random Sample
• Every element has an equal chance of
selection
• No element can be selected more than once
Systematic Random Sample
Sampling Frame
Nth Element
A simple random sample employing a sample
frame.
Stratified Random Sample
Cluster Sample
Non probability samples
•
•
•
•
•
Convenience (available to researcher)
Snowball (available connections)
Quota (stratified without randomness)
Informant (case study/social history)
Focus Groups
What’s the difference?
How important is the difference?
Probability samples can be generalized to a
population; while non-probability samples
cannot.
Non-probability offer an in depth understanding
and are most often: “I don’t know what I am
seeking until after I find it.”
Following is an illustration:
Overview of Sample Problems
Hite, S. (1987). Women in Love: A
Cultural Revolution in Progress. NY:
Alfred A. Knopf.
Laumann, E. O., Gagnon, J. H.,
Michael, R. T. & Michaels, S. (1994).
The Social Organization of Sexuality:
Sexual Practices in the United States.
Chicago: University of Chicago
Press.
Sample Size Selection
The problem with the following formula:
It is calibrated for dichotomous data. The
sample size will increase with the number of
options given to the subject.
Do NOT Forget!!!!
Regardless of what
formula one uses,
always increase the
sample size by 20%.
Excel
• RANDBETWEEN – Returns a random number
between the numbers you specify.
• RAND – Returns a random number greater
than or equal to 0 and less than 1, evenly
distributed (changes on recalculation).