Simple random sample (of size n)
A sample selected in a way that gives every different sample of size n an equal chance of being selected.
Stratified random sampling
Dividing a population into subgroups(strata) and then taking a separate random sample from each stratum. Typically the subjects within each strata are similar in some respect.
Dividing a population into subgroups and forming a sample by randomly selecting groups, including all individuals or objects in the selected groups in the sample. Hopefully, the groups selected are a good representation of the population.
systematic random sampling
A sample selected from an ordered arrangement of a population by choosing a starting point at random from the first k individuals on the list and then selecting every kth individual thereafter
Measurement or response bias
The tendency for a sample to differ from the population because the method of observation tends to produce values that differ from the true value.
The tendency for a sample to differ from the population due to systematic exclusion of some part of the population.
The tendency for a sample to differ from the population because measurements are not obtained from all individuals selected for inclusion in the sample.
A study that observes characteristics of an existing population.
A procedure for investigating the effect of conditions (which are manipulated) on a response variable.
The experimental conditions imposed by the experimenter.
A variable that is not of interest in the current study but is thought to affect the response variable.
A variable that is related both to group membership and to the response variable in such a way that its effects on the response variable cannot be differentiated from the effects of the explanatory variable on the response variable.
Holding extraneous factors constant so that their effects are not confounded (confused) with those of the experimental conditions.
Using extraneous factors to create experimental groups that are similar with respect to those factors, thereby filtering out their effect. All treatments should be applied to each group.
Random assignment of experimental units to treatments.
Ensuring that there is an adequate number of observations on each experimental treatment.
A treatment that resembles the other treatments in an experiment in all apparent ways, but which has no active ingredients.
A group that receives no treatment or one that receives a placebo treatment.
An experiment in which the subjects do not know which treatment was received but the individuals measuring the response do know which treatment was received or one in which the subjects do know which treatment was received but the individuals measuring the response do not know which treatment was received.
An experiment in which neither the subjects nor the individuals who measure the response know which treatment was received.