observational study
In this kind of study, we observe and measure specific characteristics but we don't attempt to modify the subjects being studied.
Experiment
In this kind of study, we apply some treatment and then proceed to observe its effects on the subjects.
Experimental units
Subjects in experiments are called __________ _____
Simple Random Sample
A ______ ________ _______ of n subjects is selected in such a way that every possible sample of the same size n has the same chance of being chosen.
Random sample
In this kind of sample, members from the population are selected in such a way that each individual member in the population has an equal chance of being selected.
Probability Sample
In this kind of sample, it involves selecting members from a population in such a way that each member of the population has a known (but not necessarily the same) chance of being selected.
systematic sampling
In this kind of sampling, we select some starting point and then select every kth (such as every 50th) element n the population.
convenience sampling
In this kind of sampling, we simply use results that are very easy to get.
stratified sampling
In this kind of sampling, we subdivide the population into at least two different subgroups (or strata) so that subjects within the same subgroup share the same characteristics (such as gender or age bracket), then we draw a sample from each subgroup (or
cluster sampling
In this kind of sampling, we first divide the population area into sections (or clusters), then randomly select some of those clusters, and then choose all the members from those selected clusters.
stratified
Cluster sampling uses all members from a sample of clusters, whereas ______ sampling uses a sample of members from all strata.
multistage sample design
In a _______ ____ _______, pollsters select a sample in different stages, and each stage might use different methods of sampling.
cross-sectional study
In this kind of study, data is observed, measured, and collected at one point in time.
retrospective (or case-control) study
In this kind of study, data is collected from the past by going back in time (through examination of records, interviews, and so on).
prospective (or longitudinal or cohort) study
In this kind of study, data is collected in the future from groups sharing common factors (called cohorts).
Randomization
__________ is used when subjects are assigned to different groups through a process of random selection.
replication
________ is the repetition of an experiment on more than one subject.
Blinding
_______ a technique in which the subject doesn't know whether he or she is receiving a treatment or a placebo.
Placebo effect
This occurs when an untreated subject reports an improvement in symptoms.
double-blind
The polio experiment was __________, meaning that blinding occurred at two levels: (1) The children being injected didn't know whether they were getting the Salk vaccine or a placebo, and (2) the doctors who gave the injects and evaluated the results did
Confounding
This occurs in an experiment when you are not able to distinguish among the effects of different factors. Try to plan the experiment so that this does not occur.
Completely randomized experimental design
This design assigns subjects to different treatment groups through a process of random selection.
randomized block design
In this design, a block is a group of subjects that are similar, but blocks differ in ways that might affect the outcome of the experiment. (more info on p.33)
Matched pairs design
In this design, you compare exactly two treatment groups (such as treatment and placebo) by using subjects match in pairs that are somehow related or have similar characteristics.
Rigorously controlled design
In this design, you carefully assign subjects to different treatment groups, so that those given each treatment are similar in the ways that are important to the experiment.
randomization
Use __________ to assign subjects to different groups
replication
Use ________ by repeating the experiment on enough subjects so that effects of treatments or other factors can be clearly seen.
Control, effects, variables
_______ the ____ of __________ by using such techniques as blinding, completely randomized experimental design, randomized block design, rigorously controlled design, and matched pairs design.
Sampling error
The difference between a sample result and the true population result; such an error results from chance sample fluctuations.
nonsampling error
Occurs when the sample data are incorrectly collected, recorded, or analyzed (such as by selecting a biased sample, using a defective measurement instrument, or copying the data incorrectly).