A useful distinction for quantitative variables is that they can
be discrete or continuous.
The most common type of discrete variable is a
count, in which case it must be a whole number.
Examples include family size, number of road deaths and number of
cigarettes smoked per day.
Continuous variables are defined on a continuous
scale. Examples include length, weight, parts per million of waste
material in water. Inevitably, the rounding of the measurement means
that continuous variables are often reported on a discrete scale.
For example, taxable income is measured in dollars and cents but
reported to the Tax Office rounded to the nearest whole dollar.
Similarly, when someone asks you for your height, you usually round
it to the nearest whole cm, and you do not report it on a continuous
scale even though height (length) can be measured to great accuracy
on a continuous scale.
