Census

Selecting a sample rather than obtaining information from an entire population.

Selection Bias

Tendency for samples to differ from the corresponding population as a result of systematic exclusion of some part of the population.

Measure or Response bias

Tendency for samples to differ from the corresponding population because the method of observation tends to produce values that differ from the true value.

Nonresponse bias

Tendency for samples to differ from the corresponding population because data are not obtained from all individuals selected for inclusion in the sample.

Simple Random Sample of Size N

A sample that 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 Frame

A list of the objects or individuals in the population.

Sampling Without Replacement

Once an individual from the population is selected for inclusion in the sample, it may not be selected again in the sampling process, it includes n distinct individuals from the population

Sampling With Replacement

After an individual from the population is selected for inclusion in the sample and the corresponding data are recorded, the individual is placed back in the population and can be selected again in the sample process, it might include any particular individual from the population more than once.

Stratified Sampling

Easier to implement and more cost-effective than random sampling when the entire population can be divided into a set of non-overlapping subgroups.

Strata

A subgroup in stratified sampling.

Cluster Sampling

Involves dividing the population of interest into non-overlapping subgroups.

Clusters

Non-overlapping subgroups in cluster sampling.

Systematic Sampling

A procedure that can be used when it is possible to view the population of interest as consisting of a list or some other sequential arrangement.

1 in K Systematic Sampling

When a value k is specified (e.g., k = 50 or k = 200), then one of the first k individuals is selected at random, after which every kth individual in the sequence is included in the sample.

Convenience Sampling

Using an easily available or convenient group to form a sample, don't go there because results from such samples are rarely informative, and it is a mistake to try to generalize from a convenience sample to any larger population.

Observational

A study where the investigator observes characteristics of a subset of the members of one or more existing population. The goal is usually to draw conclusions about the corresponding population or about differences between two or more populations.

Experiement

A study where the investigator observes how a response variable behaves when the researcher manipulates one or more factors. the usual goal of an experiment is to determine the effect of the manipulate factors on the response variable.

Confounding Variable

A variable that is related to both group membership and the response variable of interest in a research study.

Factors

One or more explanatory variables.

Experimental Condition or Treament

Any particular combination of values for the explanatory variables.

Design of an Experiment

The overall plan for conducting an experiment. A good design minimizes ambiguity in the interpretation of the results.

Extraneous Factor

On that is not of interest in the current study but is thought to affect the response variable

Confounded

Two factors are confounded if their effects on the response variable cannot be distinguished from one another.

Randomization

Random assignment (of subjects to treatments or of treatments to trials) to ensure that the experiment does not systematically favor one experimental condition over another.

Blocking

Using extraneous factors to create groups (blocks) that are similar. All experimental conditions are then tried in each block.

Direct Control

Using extraneous factors to create groups (blocks that are similar. All experimental conditions are then tried in each block

Control Group

A group that receives no treatment to compare with a group the receives a particular treatment.

Placebo

Something that is identical (in appearance, taste, feel, etc.) to the treatment received by the entrapment group, except that it contains no active ingredients.

Double-Blind Experiment

An experiment in which neither the subjects nor the individuals who measure the response know which treatment was received.

Single-Blind Experiement

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 on in which the subjects do know which treatment was received but the individuals measuring the response do not know which treatment was received.

Experimental Unit

The smallest unit to which a treatment is applied.

Survey

A voluntary encounter between strangers in which an interviewer seeks information from a respondent by engaging in a special type of social conversation.