## 2. What are variables and parameters?

We use the term 'variable' to represent a quantity that can have a range of values. If we have a group of several people and measure the height of each person, height is a variable and can have a different value for each person.

Some variables can have any value within a range and are termed 'continuous' variables, whilst other variables can only have certain specified values or scores and are termed 'discontinuos' or 'step' variables. A numerical ranking is an example of a discontinuous variable.

Parameters (sometimes also called 'constants') are fixed values, at least within a given context. We may have a relationship between a person's height and their shoe size. This could be described in a word equation as:

Shoe size = Height × R

Here, the quantity R has a single value. It has been derived by measuring the relationship between shoe size and height for several people. R is termed a parameter in the equation.

Constants are really special cases of parameters where they have been determined as universally-applicable quantities. For instance, in the famous equation linking mass and energy:

E = m.C^{2}

the symbol 'C' represents the velocity of light and is a constant value. The symbol 'm' represents mass, and is a variable, and determines the value of E, energy.