Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
Lecture Notes
Chapter 6: Sampling: Who, What, and How Many?
Learning Objectives
6-1 Compare and contrast probability and nonprobability sampling.
6-2 Identify and explain major nonprobability sampling methods.
Chapter Summary
This chapter begins by comparing probability and nonprobability sampling. Next, the chapter
identifies and explains major nonprobability and probability sampling methods. Then, the
Annotated Chapter Outline
I. Introduction
A. Research is a decision to sample
1. A population contains every one of the units the researcher has elected to study.
B. Probability
1. Nonprobability samples are based on a judgment by the researcher.
II. Nonprobability Sampling
A. Convenience sampling
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
1. Convenience sampling is based on convenience to the researcher.
B. Purposive or judgmental sampling
1. Purposive sampling is based on the idea that a specific person content will meet
C. Quota sampling
1. Quota sampling attempts to replicate in a sample the features the researcher
D. Network or snowball sampling
1. Network or snowball sampling is volunteer sampling that occurs when members
E. Volunteer sampling
1. Network or snowball samples are obtained by an initial group of volunteers.
III. Probability Sampling
A. Probability sampling
1. Probability sampling turning the selection of units over to a mechanism over
which the researcher has no control so that every unit has an equal chance of
B. Random sampling
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
1. Random sampling is when every unit has an equal chance of being drawn.
C. Stratified random sampling
1. Stratified random sampling is a way to “force” such groups into your sample.
D. Systematic sampling
1. Systematic sampling means sampling every nth person on a list, for example,
every 10th or every 100th person.
E. Multistage cluster sampling
1. Multistage cluster sampling works by first sampling larger units.
IV. How Big Does My Sample Have to Be?
A. Practical considerations
1. Depends on your resources.
B. Nature of your research
1. Ethical considerations.
C. Level of confidence
1. Level of statistical confidence required.
D. Homogeneity
1. Degree of sameness of the population.
V. Some Issues with Sampling Frames
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
A. Postal sampling frames
1. Eliminates the homeless and transient from the sample.
B. Telephone sampling frames
1. Random digit dialing (RDD)—that is, dialing computer-generated random
numbers in the hopes of reaching unlisted numbers.
C. Internet sampling frames
1. Sampling from the internet offers both advantages and disadvantages.
2. Internet users differ overall from the general population with respect to age,
D. Special populations
1. Problems of accessing special populations: medical conditions, military,
immigrants.
E. The future of survey sampling
1. Traditional probability sampling may be over.