Chapter 14 - Sampling Flashcards
Population
Entire group the researcher wishes to investigate (i.e.,
target population)
Element
A single member of the population
Sample
Some elements (or a subset) of the population
Sampling unit
Elements available/considered for selection at a
particular stage of the sampling process
* Unit of observation (measurement) and unit of analysis
Subject
A single member of the sample
How do we obtain representative samples?
– Define the target population
– Determine the sample frame
– Determine the sampling design/method
* Probability vs. nonprobability sampling
– Determine the appropriate sample size
– Execute the sampling process
Probability sampling
Elements in the population have a known,
nonzero chance/probability of being selected
as sample subjects
Simple random sampling
Each element has known and equal probability of selection
Systematic sampling
Randomly select initial point, then every nth element
Stratified random sampling
– Strata: distinct and non-overlapping homogeneous subgroups
– Proportionate vs. disproportionate stratified sampling
Cluster sampling
– Clusters: “natural,” relatively heterogeneous subgroups
– A common type is area sampling
– Single-stage vs. multistage cluster sampling
Double sampling
– Select a subset of the initial sample for further research
Nonprobability sampling
– Elements in the population do not have a known or
predetermined chance of being selected as subjects
* Inclusion/exclusion of elements left to the discretion of the
researcher
– Cannot generalize findings to the target population
with any measured degree of confidence
* However, may still result in a reasonably “representative”
sample
– Particularly useful when researchers are more
concerned with obtaining preliminary information in a
quick and inexpensive way than with generalizability
Convenience sampling
Elements that are most readily available
Snowball (referral) sampling
Initial respondents identify other respondents
Judgment sampling
– Selecting elements for a specific purpose
– When a limited number or category of people has the
required information
Quota sampling
– A form of stratified sampling
– Population is divided into strata, but element selection is
made on a convenience basis
Exercise 14.1
A medical inspector wants to estimate the overall
average monthly occupancy rates of the cancer
wards in 80 different hospitals which are evenly
located in the northwestern, southeastern,
central, and southern suburbs of New York City.
Simple random sampling
or
Cluster sampling
The McArthur Co. produces special vacuum cleaners… About
a thousand of these are produced every month with stamped
serial numbers and stored serially in a stock room. Once a
month, an inspector does a quality control check on 50 of these. When he certifies them as to quality, the units are released from the stock room for sale. The production and sales managers, however, are not satisfied with the quality control check since, quite often, many of the units sold are returned by customers because of various types of defects. What would be the most useful sampling plan to test the 50 units?
Simple random sampling
or
Systematic sampling
A consultant had administered a questionnaire to
some 285 employees using a simple random
sampling procedure. As she looked at the
responses, she suspected that two questions
might not have been clear to the respondents.
She would like to know if her suspicion is wellfounded.
Double sampling
The executive board of a relatively small university
located in Europe wants to determine the attitude of
their students toward various aspects of the
university. … The university specializes in the social
sciences and humanities and has 5 faculties, 6 service
departments, 8 research centers, and 2 graduate
schools. The executive board has asked you to come
up with a sampling plan.
Stratified random sampling
An applied researcher at the Ontario Police College conducted
a job analysis of police managers in Ontario. The sampling
plan was designed to ensure representation from various ranks
(e.g., Sergeant to Chief), functions (e.g., Patrol, Criminal
Investigation, Administration), and service sizes. The
researcher requested certain types and numbers of respondents
from each service. Police services chose which of their
members would participate in the survey.
Quota sampling