BHV 390 Research Methods NonProbability Sampling Techniques Kimberly

BHV 390: Research Methods Non-Probability Sampling Techniques Kimberly Porter Martin, Ph. D.

What is a Population? DEFINITION: The group to which you want to generalize your findings. IN OTHER WORDS: The larger group you are representing with your sample. OR The larger group to which your results will apply.

What is a Sample? DEFINITION A subset of the population being studied from which data is actually collected. A good sample accurately represents all kinds of elements/members in proportion to their presence in the population.

Sampling Techniques Sampling techniques are the processes by which the subset of the population from which you will collect data are chosen. There are TWO general types of sampling techniques: 1) PROBABILITY SAMPLING 2) NON-PROBABILITY SAMPLING

Non-Probability Sampling DEFINITION The process of selecting a sample from a population without using (statistical) probability theory. NOTE THAT IN NON-PROBABILITY SAMPLING • each element/member of the population DOES NOT have an equal chance of being included in the sample, and • the researcher CANNOT estimate the error caused by not collecting data from all elements/members of the population.

Types of Non-Probability Sampling 1. Convenient (or Convenience) Sampling 2. Quota Sampling 3. Judgment Sampling 4. Snowball Sampling

Convenient Sampling DEFINITION Selecting easily accessible participants with no randomization. For example, asking people who live in your dorm to take a survey for your project.

Quota Sampling DEFINITION Selecting participant in numbers proportionate to their numbers in the larger population, no randomization. For example you include exactly 50 males and 50 females in a sample of 100.

Judgment Sampling DEFINITION Selecting participants because they have certain predetermined characteristics, no randomization. For example, you want to be sure include African Americans, Euro. Americans, Latinos and Asian Americans in relatively equal numbers.

Snowball Sampling DEFINITION Selecting participants by finding one or two participants and then asking them to refer you to others. For example, meeting a homeless person, interviewing that person, and then asking him/her to introduce you to other homeless people you might interview.

Study Guide Population Sample Probability sampling Non-probability sampling Convenient sample Quota sample Judgment sample Snowball sample