Different types of measurements in Epidemiology
As we know, epidemiology is about distribution and determinants of diseases
in populations and means to prevent them. That said, it's important to
measure frequencies of diseases in populations. One possible way would be to
simply do a head count of people with certain illnesses. As you may see,
such head counts are of limited usage because this way you cannot compare
two populations or existence or state of change of diseases in a population
over time. Therefore, we need both base populations or a frame of reference
and a time frame to deal with.
There are essentially three forms of mathematical parameters that can be
used while comparing numbers and entities. First, ratio measurements that
essentially measure two quantities that have no inherent relationship with
each other. For example, male:female ratio in a population. Second,
proportion measures how much of the denominator is contained within the
numerator. For example, what percent of men in a population have heart
disease might be such a question. Finally, Rate indicates a measure where an
element of time is involved in indicating how things change over time.