
variable
A measurement that changes from one observation to the next. A quality or characteristic that changes from individual to individual.

constant
A measurement that stays the same from one observation to the next.

sample
A subset of measurements from a population. Defined in terms of the population.

random sample
A type of sample that is selected so that every score in the population has an equal chance of being included.

population
A collection or set of measurements of a variable that share some common characteristics. It is determined by the researcher's interest of study.

descriptive statistical procedure
Statistical procedures that are used to organize and summarize the measurements in samples and populations.

inferential statistical procedure
Statistical procedures that are used to make educated guesses (inferences) about populations based on random samples from the populations.

validity
Refers to how well the measurement rule actually measures the variable under consideration as opposed to some other variable.

reliability
An index of how consistently the rule assigns the same number to the same observation.

measurement
The use of a rule to assign a number to a specific observation of a variable.

category property
Observations assigned the same number are in the same category, and observations assigned different numbers are in different categories. (Properties of Numbers used as measurements)

ordinal property
When the numbers can be used to order the observations from those that have the least of the variable being measures to those that have the most. (Properties of Numbers used as measurements).

equal intervals property
Whenever two observations are assigned measurements that differ by exactly one unit, there is always an equal interval (difference) between the observations in the actual variable being measured. (Properties of Numbers used as measurements)

absolute zero property
A value of zero is assigned as a measurement only when there is nothing at all of the variable that is being measured. (Properties of Numbers used as measurements)

nominal scale
When the numbers assigned by the measurements rule have only the category property.

ordinal scale
When the measurement rule assigns numbers that have the category and the ordinal properties, but no other properties.

interval scale
When the numbers assigned as measurements have the category, ordinal, and equal intervals properties, but not an absolute zero property.

ratio scale
When the numbers assigned by the measurement rule have all four properties: category, ordinal, equal interval, and absolute zero.

