Sampling Flashcards
target population (reference population):
refers to the group of individuals to which results of the study are applied to; who we are going to study
population:
the general group of people from whom information is needed
accessible population
the actual population of subjects available to be chosen for a study. This group is usually a nonrandom subset of the target population.
the cases included in the study are the “____”
sample
sampling bias
bias that occurs when individuals who are selected for a sample over-represent or underrepresent the underlying population characteristics
sample:
a collection of subjects (a noun)
simple random sample:
A probabilistic sampling method in which each potential subject has an equal chance of being selected
inclusion criteria:
A list of specific attributes that will make an individual (or a unit of analysis such as an organization) eligible for participation in a specific study.
exclusion criteria:
A list of characteristics that may influence, or “confound,” the outcomes of a study; researchers use these criteria to eliminate individuals (or units of analysis such as an organization) with these characteristics as subjects in a study
sampling frame:
A list of potential subjects obtained from various public or private sources
extraneous variables:
Individual, organizational, or environmental characteristics other than the factor of interest (i.e., test, predictor, intervention) that may influence the outcome of a study
sampling:
the method for selecting individuals for a study, also called “selection”
probabilistic sampling:
Methods for choosing subjects that use a random selection process to increase the chance of obtaining a sample that accurately represents the population from which it is drawn
nonprobabilistic sampling:
Methods for choosing subjects that do not use a random selection process; as a result, the sample may not represent accurately the population from which it is drawn.
cluster sampling:
A form of probability sampling in which large subgroups (clusters) are randomly selected first, and then smaller units from these clusters are successively chosen; also called multistage sampling.
convenience sampling:
A nonprobability sampling procedure, involving selection of the most available subjects for a study
purposive sampling:
A nonprobability sample in which subjects are specifically selected by the researcher on the basis of subjective judgment that they will be the most representative
snowball sampling:
A nonprobability sampling method in which subjects are successively recruited by referrals from other subjects.
stratified random sampling:
A probabilistic sampling method in which subgroups of a population are identified and randomly selected to ensure their inclusion in a study
systematic sampling:
A probabilistic sampling method in which the first subject is randomly selected from a group organized according to a know identifier (such as birth date) and then all remaining subjects are chosen based on their numerical distance from the first individual.
assignment:
putting subjects into groups, also called “allocation”
block assignment
An assignment method in which the number of individuals in each group is predetermined; investigators randomly assign subjects to one group at a time until each quota is met.
masked (blinded):
(1) In diagnostic test and clinical measure papers, the lack of knowledge about previous test/measure results; (2) in prognostic factor papers, the lack of knowledge about exposure status; and (3) in intervention papers, the lack of knowledge about to which group a subject has been assigned
matched assignment:
An assignment method in which subjects are first divided into subgroups based on a specific characteristic such as age, gender, and so forth; members of each subgroup are then randomly assigned to each group in the study to balance the characteristics across the groups.
random assignment by individual:
An assignment method in which each subject is randomly allocated to a group based on which side of a coin lands upright or which number is pulled from a hat.
systematic assignment:
An assignment method in which subjects count off the group numbers until everyone is assigned
primary data:
Data collected in real time from subjects in a study; used in prospective research designs
secondary data:
Data that have been collected previously by others for non-research purposes that are used by investigators to answer a research question; used in retrospective research designs.
sampling error:
The difference between an observed statistic from a sample and the population parameter
type II error:
Failure to reject the null hypothesis, avoidable.
power:
The ability of a statistical test to find a significant difference that really does exist; the probability that a test will lead to rejection of the null hypothesis.
subjects:
the term used for people in a research study
cases:
the term used for records
specimen:
the term used in inanimate objects
subjects are identified as detailed as needed to meet the _____ of the study
objective
inclusion criteria are used to identify the desired ______, examples are ___________________.
characteristics; age, occupation, dx, gender, etc
exclusion criteria are used to ______ persons with characteristics or complications that the researcher does not want to study; examples are ____
eliminate; other conditions, mental problems, age, gender, etc
Once a population with the desired _____ factors is identified, the researcher must determine an ______ population from which subjects may realistically be recruited.
inclusion, accessible
After identifying the population what 3 things need to be done?
- recruit the subject
- review for exclusion factors
- provide informed consent to participate
Once the subject agrees to participate what happens next?
they are assigned to a study group
The method of assignment is critical in determining the ______ of a research study
rigor (control)
What type of sampling techniques uses random selection to assign to groups? What type of rigor does it give the study?
probabilistic, higher level of rigor
When randomization is not possible what type of sampling is done? What type of rigor is indicated?
nonprobabilistic, lower rigor
If assignment methods are weak, the critical review language will say it is a “_________”
threat to validity
Is a larger sample size always better?
no
______ has given guidelines to the number of subjects needed to meet the researcher selected significance level.
statistical analysis
_________ is the term given to a statistical formula that considers sample size, significance, and error level; normally a researcher proposes this.
power analysis
A good rule of thumb is that for every variable being analyzed, a sample needs ____ subjects
15-20
Type I error
Incorrectly reject the null hypothesis
