For some purposes, neither height nor weight alone is of interest.
Epidemiologists are often more interested in the @dfn{body mass index} which
can sometimes be used as a predictor for clinical conditions.
-The body mass index is defined as the weight of the person in kg divided
+The body mass index is defined as the weight of the person in kilograms divided
by the square of the person's height in metres.
@footnote{Since BMI is a quantity with a ratio scale and has units, the term ``index''
is a misnomer, but that is what it is called.}