Typical Sampling Techniques

PMR designs studies using the following sampling techniques:

• RDD samples – simple random samples developed with randomly generated numbers attached to telephone exchanges to make certain to include both listed and unlisted households in the sample
• Nationwide listed random samples – selected randomly from a listing of all phone numbers in US phonebooks
• Segmented listed samples – random samples segmented by age, gender, ethnicity, county, state, etc.
• Stratified sampling - Can be used with RDD sampling when U.S. Census data on regions are available. In stratified sampling, the population is first divided into homogeneous groups, also called strata. Then, elements from each stratum are selected at random according to one of the two ways:
  • the number of elements drawn from each stratum depends on the stratum's size in relation to the entire population ("proportionate" sampling)
  • the number of elements sampled from each stratum is not proportionate to the size of the stratum ("disproportionate" sampling); in this case, an equal number of elements is typically drawn from each stratum and the results are weighted according to the stratum's size in relation to the entire population.
• Cell phone samples – to enhance the inclusion of all age groups in telephone surveys

Samples from lists provided by clients:

• Convenience samples – e.g. samples of persons who are entering a store or restaurant
• Contact list samples – from lists provided by clients or vendors, usually cell phone numbers or e-mail addresses

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