ABSTRACT
An important aspect of civil engineering work is the determination of quantities
such as forces, flows, rainfall intensities or wind speeds that, by their nature, will
have a range of values rather than being fixed. It is convenient to treat variables as
either continuous, discrete or categorical. Continuous variables are measured on
some underlying continuous scale even though they are recorded to a fixed number
of decimal places. Examples include temperatures, pressures, tensile strengths and
soil porosity. Discrete variables usually take non-negative integer values and in
most applications are counts of numbers of occurrences. For example, the number
of road traffic accidents per year, the number of hurricanes per year, the number of
asbestos-type particles in fixed volumes of air and the number of defective items in
random samples of a product. Categorical variables include colour, day of week,
type of mineral and supplier in situations where there are several. In some cases
categorical variables may be ordered in some sensible manner such as levels of
agreement with a statement in a survey.
