27 terms

Stats Chapter 2

STUDY
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Observational Study
investigator observes characteristics of a subset of the members of one or more exsisting populations
experimental study
investigator observes how a response variable behaves when the researcher manipulates one or more explanatory variables
confounding variable
if two factors or their effects on response variable cannot be distinguished from one another
selection bias
when the was a sample is selected systematically excludes part of the population
measurement (response) bias
when the method of observation tends to produce values that systematically differ from the true value in some way
non-response bias
when responses are not obtained from all individuals selected for inclusion in the sample
simple random sample
a sample which is selected from a population in a way that ensures that every different possible sample of the desired size has the same chance of being selected
sampling without replacement
once an individual has been selected for inclusion in a sample, it may not be selected again in the sampling process
sampling with replacement
after an individual is selected for a sample and data is recorded, the individuals are placed back into the population and can be picked again
stratified sampling
entire population can be divided into a set of non-overlapping subgroups and separate random samples are taken from each subgroup
strata
non-overlapping subgroups in a population
cluster sampling
dividing population into non-overlapping subgroups and the groups are then selected at random, all individuals in the group are included in the sample
systematic sampling
a k value is specified, and one of the first k individuals is selected at random, after which every kth individual in the sequence is used in the sample
voluntary response sampling
the type of sampling that we do not use
experiment
planned intervention undertaken to observe the effects of one or more explanatory variables on a response variable
design
overall plan for conduction experiment
extraneous factor
one that is not of interest in the current study but is thought to affect the response variable
confounding variables
if two factors and their effects on the response variable cannot be distinguished from one another
randomization
random assignment to ensure that the experiment does not systematically favor one experimental condition over another
blocking
using extraneous factors to create groups that are similar. All experimental conditions are then tried on each group
direct control
holding extraneous factors constant so that their effects are not confounded with those of the experimental conditions
replication
ensuring that there is an adequate number of observations for each experimental condition
control group
group that does not receive experimental treatment
placebo
something which is identical to the treatment received by the treatment group except that it contains no active ingredients
double-blind
neither the subjects nor the individuals who measure the response variable know which treatment was received
single-blind
either the subjects know which treatment they received, or the individuals who measure the response variable know which treatment the subject received, but not both
survey
voluntary encounter between strangers in which the interviewer seeks information from a respondent by engaging in a special type of conversation
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