Sampling Design

Sampling Design




Sampling
The process of obtaining information from a subset (sample)
of a larger group (population)
The results for the sample are then used to make estimates
of the larger group
Faster and cheaper than asking the entire population
Two keys
1. Selecting the right people
Have to be selected scientifically so that they are
representative of the population
2. Selecting the right number of the right people
To minimize sampling errors I.e. choosing the wrong
people by chance




SAMPLING
• Sample -- contacting a portion of the
population (e.g., 10% or 25%)
– best with a very large population (n)
– easiest with a homogeneous population
• Census -- the entire population
– most useful is the population ("n") is small
– or the cost of making an error is high




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, Population Vs. Sample
Population of Interest




Population Sample
Sample

Parameter Statistic

We measure the sample using statistics in order to draw
inferences about the population and its parameters.




Characteristics of Good Samples
• Representative

• Accessible

• Low cost




…this (bad)…


Sample
Population




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