a 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
divide the population into smaller groups. These clusters should mirror the characteristics of the population. Then choose an SRS of the clusters. All individuals in the chosen clusters are included in the sample.
Completely randomized design
when the treatments are assigned to all the experimental units completely by chance
two variables are associated in such a way that their effects on a response variable can't be distinguished from each other.
controlling for as many lurking vars as possible, by using a comparative design and making sure the only difference between the groups is the treatment administered.
a experimental group that serves as a baseline for comparing the effects of other treatments. may be a placebo, commonly used to measure the difference between psychological and physical effects.
an experiment in which neither the subject nor the administrator that measures the response variable know which treatment a subject received
person, a plot of land, a machine, etc. that forms the 'material' on which an experiment is performed.
a variable that is not among the explanatory or response variables in a study but that may influence the response variable.
a form of blocking for comparing just two treatments. In some, each subject receives both treatments in a random order. In others, the subjects are matched in pairs as closely as possible, and each subject in a pair is randomly assigned to receive one of the treatments
when a selected individual can't be contacted or refuses to cooperate, example of a nonsampling error
observes individuals and measures variables of interest but does not attempt to influence the responses
describes the fact some subjects respond favorably to any treatment(psychological effect)
randomized block design
forming blocks consisting of similar individuals. random assignment of treatments
use enough experimental units in each group so that any differences in the effects of the treatments
the part of the population from which we collect information. we use information from a sample to draw conclusions about an entire population
mistakes while taking a sample, that lead to inaccurate information about a population
stratified random sample
classify the population into similar individuals , then get an SRS from each strata
occurs when some members of the population are left out of the sampling; a type of sampling error
voluntary response samples
people decide whether to join a sample; biased by people with strong opinions