Key Practicle Terms

Range The maximum and minimum values of the independent or dependent variables. For example, a range of distances may be quoted as either: ‘from 10 cm to 50 cm’ or ‘from 50 cm to 10 cm’.

Repeatable A measurement is repeatable if the original experimenter repeats the investigation using same method and equipment and obtains the same results.

A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained.

This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading.

A line graph, not necessarily on a grid, that shows the general shape of the relationship between two variables. It will not have any points plotted and although the axes should be labelled they may not be scaled.

This is the value that would be obtained in an ideal measurement.

The interval within which the true value can be expected to lie, with a given level of confidence or probability eg “the temperature is 20 °C ± 2 °C, at a level of confidence of 95%”.

Suitability of the investigative procedure to answer the question being asked. For example, an investigation to find out if the rate of a chemical reaction depended upon the concentration of one of the reactants would not be a valid procedure if the temperature of the reactants was not controlled.

A conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning.

These are physical, chemical or biological quantities or characteristics

Categoric variables have values that are labels eg names of plants or types of material or reading at week 1, reading at week 2 etc.

Continuous variables can have values (called a quantity) that can be given a magnitude either by counting (as in the case of the number of shrimp) or by measurement (eg light intensity, flow rate etc).

A control variable is one which may, in addition to the independent variable, affect the outcome of the investigation and therefore has to be kept constant or at least monitored.

The dependent variable is the variable of which the value is measured for each and every change in the independent variable.

The independent variable is the variable for which values are changed or selected by the investigator.

A nominal variable is a type of categoric variable where there is no ordering of categories (eg red flowers, pink flowers, blue flowers)