Sampling for Research
Types of Research
• Quantitative– the collection & analysis of data to describe,
explain, predict, or control phenomena of interest• Qualitative– the collection, analysis, & interpretation of
comprehensive narrative and visual data to gain insights into particular phenomenon of interest
• Mixed-Methods
Samples for Quantitative Studies
• Generalizability– Sample chosen should be representative of the
population being examined• Sample Size– The larger the population, the smaller %age
required to get a representative sample• 50% for a sample of 500, 20% for a sample of 1,500
– For smaller populations (n=100 or fewer), the entire population is typically sampled.
Samples for Quantitative Studies
The selection process itself is critical. For example, a voter survey that systematically excluded a particular race, class or gender would be worthless...and there are a host of other ways to ruin, or bias, a sample.
Samples for Quantitative Studies
• Sample Error– A random, unknown characteristic of the sample– causes the sample to not be as representative as
1st thought• Sample Bias– A systematic sampling error– Typically caused by the researcher
Samples for Quantitative Studies
Methods of Sampling:• Simple Random Sample - every member of the
population has an equal chance of being selected
Samples for Quantitative StudiesMethods of Sampling:
• Stratified Sample - Population is divided into groups. Then a random sample is taken from each group
Samples for Quantitative Studies
Methods of Sampling:• Cluster Sample - Population is divided into groups.
Then an entire group is randomly chosen with all members of the randomly chosen group used in the sample
Non-Random Sampling MethodsNon-Random Methods of Sampling:
• Convenience Sample - A sample of well...convenience. Not scientific, just easy. Conclusions about the population cannot be drawn from this type of sample.
• Purposive Sample • Judgment sampling• The process of selecting a sample that is believed
to be representative of a given population. • Quota Sample – Process of selecting a sample
based on required, exact numbers (quotas) of individuals or groups with varying characteristics.