Key Terms

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Part 4: Obtaining Study Subjects and Collection of Data

Chapter 11: Populations and Samples

Key Terms

accidental sampling

see convenience sampling

cluster random sampling

A random sampling process that involves two or more stages. The population is first listed by clusters or categories (e.g., hospitals) and then the sample elements (e.g., hospital administrators) are randomly selected from these clusters.

cohort study

A special type of longitudinal study in which subjects are studied who have been born during one particular period or who have similar backgrounds.

convenience sampling (accidental sampling; incidental sampling)

A nonprobability sampling procedure that involves the selection of the most readily available people or objects for a study.

cross-sectional study

A research study that collects data on subjects at one point in time.

disproportional stratified sampling

Random selection of members from population strata where the number of members chosen for each stratum is not in proportion to the size of the stratum in the total population.

element

A single member of a population.

incidental sampling

see convenience sampling

judgmental sampling

see purposive sampling

longitudinal study

Subjects are followed during a period in the future; data are collected at two or more different time periods.

network sampling

see snowball sampling

nonprobability sampling

A sampling process in which a sample is selected from elements or members of a population through nonrandom methods; includes convenience, quota, and purposive.

power analysis

A procedure that is used to determine the sample size needed to prevent a Type II error.

probability sampling

The use of a random sampling procedure to select a sample from elements or members of a population; includes simple, stratified, cluster, and systematic random sampling techniques.

proportional stratified sampling

Random selection of members from population strata where the number of members chosen from each stratum is in proportion to the size of the stratum in the total population.

purposive sampling (judgemental sampling)

A nonprobability sampling procedure in which the researcher uses personal judgment to select subjects that are considered to be representative of the population.

quota sampling

A nonprobability sampling procedure in which the researcher selects the sample to reflect certain characteristics of the population.

sampling bias

(1) The difference between sample data and population data that can be attributed to a faulty selection process; (2) a threat to the external validity of a research study that occurs when subjects are not randomly selected from the population.

sampling error

Random fluctuations in data that occur when a sample is selected to represent a population.

sampling frame

A listing of all the elements of the population from which a sample is to be chosen.

simple random sampling

A method of random sampling in which each element of the population has an equal and independent chance of being chosen for the sample.

snowball sampling (network sampling)

A sampling method that involves the assistance of study subjects to help obtain other potential subjects.

stratified random sampling

A random sampling process in which a sample is selected after the population has been divided into subgroups or strata according to some variable of importance to the research study.

systematic random sampling

A random sampling process in which every kth (e.g., every fifth) element or member of the population is selected for the sample.

table of random numbers

A list of numbers that have been generated in such a manner that there is no order or sequencing of the numbers. Each number is equally likely to follow any other number.

volunteers

Subjects who have asked to participate in a study.

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