The discipline has two main strands:
• descriptive epidemiology, which measures health phenomena in a population;
• analytic epidemiology, which investigates the possible causes of disease.
When studying biological phenomena, we must bear in mind that they are not governed by chance. It is only the sheer number of possible combinations that creates the illusion of randomness. Mathematical tools devised for independent events must therefore retain their status as models. Their users must guard against purely mathematical interpretations divorced from realities on the ground.
