L2.1
BIOSTATISTICS I
(PUBH4401)
TOPIC 2
SUMMARISING AND
PRESENTING DATA
Most studies collect more data than is possible to interpret just by
looking at the raw data.
Usually, the data are summarised and
presented in a way which helps to reveal the true patterns in the
data.
2.1 Types of variables
A
variable
is a characteristic or measurement that varies from one subject to another.
It is useful to distinguish between four types of variables.
Qualitative

nominal
The variable has categories or levels with no natural order;
e.g. sex, country of birth.
Qualitative

ordinal
The variable has categories or levels with a natural order;
e.g. pain (none, mild, moderate, severe).
Quantitative

discrete
The values are numerical but only certain values are
possible; e.g. household size, number of children.
Quantitative

continuous
The values are numerical and all values in some
continuous range are possible; e.g. blood pressure, weight.
Quantitative
variables are called
scale
variables in SPSS Statistics.
A
qualitative
variable is also called a
categorical
or
attribute
variable.
A
qualitative
variable with only
two
possible values is also called a
binary
or
dichotomous
variable; e.g. male/female, dead/alive, yes/no.