Research Sampling
Use the M&Ms to illustrate the following sampling groups:
Differentiate between your entire population and your accessible population
Probability Sampling
1.
2.
3.
4.
Simple Random
Systematic
Stratified Random
Cluster
Nonprobability Sampling
1.
2.
3.
4.
Convenience
Quota
Purposive
Snowball
Probability
1.
Simple random – includes a listing of all elements in accessible population
a. Elements area randomly selected for inclusion
2. Systematic Random – used when sampling frame has no meaningful underlying order or pattern
a. Calculate sampling interval (k) by dividing desired sample size (n) into number of elements in population
b. Randomly choose a starting place in sampling frame
c. Select every kth element until desired sample size is achieved
3. Stratified Random – stratum is a mutually exclusive segment of population that is defined by one or more
characteristics
a. Once sampling frame has been stratified, elements are randomly selected from each strata using simple
or systematic random sampling processes.
4. Cluster – variation of random sampling that is used when population of interest is widely scattered
geographically and it would be difficult, if not possible, to develop a sampling frame
a. Sampling is done in 2 or more stages; grouped units referred to as clusters
Nonprobability
1. Convenience – “accidental” sample; comprised of elements that meet established eligibility criteria and are
conveniently available to researcher
a. Recruiting participants who are in the right place at the right time
2. Quota – thought of as stratified convenience sampling
a. Identifying relevant strata as well as desired number of elements from each stratum
b. Once this is done, the use of convenience sampling is implemented.
3. Purposive – judgmental sampling; researcher uses personal knowledge of a population to consciously select
(handpick) the elements that will constitute the study sample
4. Snowball – network sampling; initial sample members are asked to identify and refer or recruit others who meet
the eligibility criteria into the study.
a. Initial sample members are usually chosen by purposive sampling