27 terms

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