4 Flashcards
census
Study that attempts to collect data from every individual in the population. (p. 221)
sample
Subset of individuals in the population from which we collect data. (p. 221)
population
In a statistical study, the entire group of individuals we want information about
sample survey
Study that uses an organized plan to choose a sample that represents some specific population. We base conclusions about the population on data from the sample.
convenience sampling
Sample selected by taking from the population individuals that are easy to reach
voluntary response sampling
A sample that consists of people who choose to be in the sample by responding to a general invitation. Voluntary response samples are sometimes called self-selected samples.
The design of a statistical study shows bias if
it is very likely to underestimate or very likely to overestimate the value you want to know
random sampling
Using a chance process to determine which members of a population are chosen for the sample.
simple random sample
Sample chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample
stratified random sampling
Sample obtained by classifying the population into groups of similar individuals, called strata, then choosing a separate SRS in each stratum and combining these SRSs to form the sample
cluster sampling
Sample obtained by classifying the population into groups of individuals that are located near each other, called clusters, and then choosing an SRS of the clusters
undercoverage
Occurs when some members of the population are less likely to be chosen or cannot be chosen in a sample
nonresponse
Occurs when an individual chosen for the sample can’t be contacted or refuses to participate.
wording of questions
An important influence on the answers given in a survey. Confusing or leading questions can introduce strong bias, and changes in wording can greatly change a survey’s outcome
response bias
Occurs when there is a consistent pattern of inaccurate responses to a survey question
observational study
Study that observes individuals and measures variables of interest but does not attempt to influence the responses
confounding
When two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other
experiments
A study in which researchers deliberately impose treatments on individuals to measure their responses.
placebo
A treatment that has no active ingredient but is otherwise like other treatments
treatment
Specific condition applied to the individuals in an experiment. If an experiment has several explanatory variables, a treatment is a combination of specific values of these variables
experimental unit
The object to which a treatment is randomly assigned. When the experimental units are human beings, they are often called subjects.
subjects
Experimental units that are human beings.
factor
Explanatory variable in an experiment
level
Specific value of an explanatory variable (factor) in an experiment
comparison
Experimental design principle. Use a design that compares two or more treatments.
control group
Experimental group whose primary purpose is to provide a baseline for comparing the effects of the other treatments.
placebo effect
Describes the fact that some subjects respond favorably to any treatment, even an inactive one (placebo).
double-blind
An experiment in which neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received
single-blind
An experiment in which either the subjects or those who interact with them and measure the response variable, but not both, know which treatment a subject received
random assignment
Experimental design principle. Use chance to assign experimental units to treatments
control
Experimental design principle that mandates keeping other variables that might affect the response the same for all experimental units
replication
Experimental design principle
completely randomized design
Design in which the experimental units are assigned to the treatments completely by chance
block
Group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments
randomized block design
Experimental design begun by forming blocks consisting of individuals that are similar in some way that is important to the response.
matched pairs design
Common form of blocking for comparing just two treatments
sampling variability
The fact that different random samples of the same size from the same population produce different estimates
nference
Drawing conclusions that go beyond the data at hand.
margin of error
The difference between the point estimate and the true parameter value will be less than the margin of error in C% of all samples, where C is the confidence level
statistically significant
When the observed results of a study are too unusual to be explained by chance alone, the results are called statistically significant.`
anonymity
The names of individuals participating in a study are not known even to the director of the study
confidential
A basic principle of data ethics that requires that an individual’s data be kept private
informed consent
Basic principle of data ethics that states that individuals must be informed in advance about the nature of a study and any risk of harm it may bring.
institutional review board
Board charged with protecting the safety and well-being of the participants in advance of a planned study and with monitoring the study itself.
inference about cause and effect
Conclusion from the results of an experiment that the treatments caused the difference in responses
inference about a population
Conclusion about the larger population based on sample data. Requires that the individuals taking part in a study be randomly selected from the population of interest.
