What is epidemiology?

If you wanted to know about adverse heath outcomes in human population, you need to study human population. You can make excellent study on the rodents for the example, even the best of such study means we have to extrapolate from species to another, and therefore the study on human being is critical. Epidemiology plays this role.

What is epidemiology? It is the study of how disease distributes in human populations and what determines differences in disease risk among different population subgroups. Why one group of people have high risk of developing disease than another. What we can learn from that? How that can help us to prevent diseases? And if we turn on how the epidemiology is use, there are many uses in which three we will shown here. First the epidemiology helps us to assess the magnitude of the community burden of disease. How much disease? What type of disease in our community? Second the epidemiology helps us to identify the causes of human disease. A critical factor if we going to prevent disease. And finally the epidemiology is use to study the effectiveness of different types of  treatments.

In this presentation/writes up, I’m going to focus in the second use of the epidemiology; to identify the causes of human disease. Underlying all of this is a basic assumption that disease is not randomly distributed in human population. That is some people have a higher risk of disease than others. And what we want to do is to account for why the risk is higher in some people than another in orders to identify factors than can be modified in order to prevent the disease.

You see here some “facts” about Carrots: 

1. Nearly all sick people have eaten carrots. Obviously the effects are cumulative.
2. An estimated 99.9% of people who die from cancer and heart disease have eaten carrots.
3. 99.9% of people involved in car crashes ate carrots within 60 days of their accidents.
4. 93.1% of juvenile delinquents come from homes where carrots are served regularly. And finally, 
5. Among people born in 1839 who ate carrots, there has been a 100% mortality rate. 

How is epidemiology and epidemiologist go about their work? We basically have two steps process to be seen here. First, we try to determine what is there an association between an exposure and the disease or adverse health outcome. If we demonstrate there is an exposure then try to determine whether the observed association reflects a causal relationship of the exposure and the health outcome.  I will first focus on the first step in epidemiology reasoning to determine whether there is an association  between an exposure and a disease or adverse health outcome.

This a quotation from Greek physician Galen who was well recognised as an excellence physician. He wrote as follows about the treatment that he provided;

“All who drink of this treatment recover in a  short time, except those whom it does not help, who all die, it is obvious, therefore, that it fails only in incurable cases”.

His excellent reputation may very well be build on the logic inclusiveness because we have here a hypothesis that could not be falsify. There is no way to proving this, the ascent on what we do in science and epidemiology is to developed hypothesis that we can test and either confirm them or refute them. This is an essential.

Now, we might shuffle in looking at this lists. We might ask what a real problem here? The problem is there is no comparison group. This data were given without knowing what is the percentage in the general population who eat carrot. So underlying the question the epidemiology addresses is the need for comparison. And I would like to stress this in this write up.