categorical (qualitative) variable:A variable having values that indicate into which of several categories a population unit belongs.

census:An examination of all the units in a population.

cluster sampling (multistage cluster sampling):A sampling design in which we sequentially cluster population units into subpopulations.

descriptive statistics:The science of describing the important aspects of a set of measurements.

finite population:A population that contains a finite number of units.

frame:A list of all of the units in a population. This is needed in order to select a random sample.

infinite population:A population that is defined so that there is no limit to the number of Units that could potentially belong to the population.

interval variable:A quantitative variable such that ratios of its values are not meaningful and for which there is not an inherently defined zero value.

measurement:The process of assigning a value of a variable to each of the units in a population or sample.

nominative variable:A qualitative variable for which there is no meaningful ordering, or ranking, of the categories.

nonresponse:A situation in which population units selected to participate in a survey do not respond to the survey instrument.

ordinal variable:A qualitative variable for which there is a meaningful ordering or ranking of the categories.

population:A set of existing units (people, objects, events, or the like) that we wish to study.

process:A sequence of operations that takes inputs and turns them into outputs.

qualitative (categorical) variable:A variable having values that indicate into which of several categories a population unit belongs.

quantitative variable:A variable having values that are numbers representing quantities.

random number table:A table containing random digits that is often used to select a random sample.

random sample:A sample selected so that, on each selection from the population, every unit remaining in the population on that selection has the same chance of being chosen.

ratio variable:A quantitative variable such that ratios of its values are meaningful and for which there is an inherently defined zero value.

response bias:A situation in which survey participants do not respond truthfully to the survey questions.

runs plot:A graph of individual process measurements versus time.

sample:A subset of the units in a population.

sampling without replacement:A sampling procedure in which we do not place previously selected units back into the population and, therefore, do not give these units a chance to be chosen on succeeding selections.

sampling with replacement:A sampling procedure in which we place any unit that has been chosen back into the population to give the unit a chance to be chosen on succeeding selections.

statistical control:A state in which a process does not exhibit any unusual variations. Often this means that the process displays a uniform amount of variation around a constant, or horizontal, level.

statistical inference:The science of using a sample of measurements to make generalizations about the important aspects of a population.

statistical process control (SPC):A method for analyzing process data in which we monitor and study the process variation. The goal is to stabilize (and reduce) the amount of process variation.

strata:The subpopulations in a stratified sampling design.

stratified random sampling:A sampling design in which we divide a population into nonoverlapping subpopulations and then select a random sample from each subpopulation (stratum).

systematic sample:A sample taken by moving systematically through the population. For instance, we might randomly select one of the first 200 population units and then systematically sample every 200th population unit thereafter.

undercoverage:A situation in sampling in which some groups of population units are underrepresented.

variable:A characteristic of a population unit.