# Glossary

central value

The value for your data. Usually the mean, but occasionally something else.

continuous variable

A quantity, like time or mass, whose values are continuous: they can take on any value with an infinite number of decimal places.

discrete variables

Variables, such as dice rolls or counting atoms, that can only take on specific values. You cannot have half an atom!

indicated measurement

The indicated measurement is the observational result of a continuous variable as reported by your measuring device, which has a limited precision.

parameter

A property of the entire population. The average height of all the people on Earth would be a parameter. Parameters are often measured by statistics which are based off samples.

percent uncertainty

The uncertainty on a measurement divided by the mean. Generally a more useful quantity than percent error which requires a true value.

population

The complete set of persons, places, things, etc. understudy. Often this set is too large (it may even be infinite) to study in its entirety. As such, we usually sample.

Measuring time, for example, is a sample. You are doing a few measurements of the infinite number of possible values.

sample

A subset of the population under study.

Measuring time, for example, is a sample. You are doing a few measurements of the infinite number of possible values.

statistic

A number that represents a property of the sample. Examples could be mean, median, or standard deviation.

statistical uncertainty

Uncertainty arising from any measurement of a continuous variable. The true value is not only unknown, but unknowable due to its infinite number of digits. Moreover, there is intrinsic randomness from measurement to measurement.

systematic uncertainty

A consistent difference between the indicated and true values, usually arising from a miscalibrated instrument or neglected effect. A systematic uncertainty is always in the same direction as opposed to the random bouncing around characteristic of statistical uncertainties.

true measurement

The unknowable actual value of a continuous variable including the infinite number of decimal places. 