The etiology (Greek αἰτία AITIA "Cause" λόγος lógos "reason, teaching ") is a branch of medicine (especially epidemiology ) and psychology (especially clinical psychology ), which deals with the cause of the development of diseases. In a similar meaning, the expression etiopathogenesis (Greek γένεσις genesis " origin, creation " ) is used, where pathogenesis denotes the origin and development of disease (see Pathology ).

In philosophy, especially in some ancient philosophical schools, the term aetiology is the study of the causes in general. The adjective means etiologically accordingly in general: " the causes ", " reason ", " the causal origin " or " the causal derivation " concerning or explanatory.

In medical parlance, the term etiology:

  • Defined in general pathology the study of the causes of diseases (etiology narrow sense );
  • In the clinical sense of the totality of the factors that have led to a given disease ( pathogenesis narrow sense ).

The three " C" of the etiology

There are three basic methods of aetiology, and each knows a different degree of certainty with which the cause of a disease or condition is found. Knowing the " three C" can also help the patient while not losing as a serious diagnostic head, but rational to reconsider his behavior. This is especially true with regard to the questions "What have I done wrong? " Or " Am I to blame for my suffering? ".

Usually operates the medical (and also scientific ) research so that first a correlation ( Correlatio ) is detected. Upon further examination one can - or not - to find out whether there is a cause-effect relationship ( Contributio ). It is often the last step, a causal relationship ( Causa ) to find out.


Causa (Latin for " cause" ): With more frequent and better studied medical phenomena one can seek a disease by " causal " reasons. That is, when the event A occurs, then the event B must occur. Examples are:

  • Smoking: Nicotine consumption always decreases the diameter of blood vessels and thus deteriorated inter alia, the blood flow to the body tissues. This means that one end of nicotine consumption always has an improved result in bleeding.


In Contributio (Latin for " promotion, contribution" ), there is still a strong correlation in terms of a cause-effect relationship, but this is not as strong as in the previous category. In general, if event A arrives, then event B meets more frequently than usual factor A thus contributes to state B at.

  • Example: Not every smoker gets lung cancer, but smokers get lung cancer more often than Non smoking. So, stop smoking means that, ceteris paribus, the likelihood of developing lung cancer decreases.


The correlation ( Correlatio, Latin for " correlation, coherence " ) is also used on rare diseases as diseases that have no clear or explored cause-effect relationships. Once you So in a newspaper report of " It was ... a relationship found between migraine and heart problems," reads, one should think of the correlation. No one was able to describe or demonstrate whether migraine heart problems or heart problems can cause migraine, but it was only found that people with property A often also possess the property B and vice versa. The correlation is different (effect) does not distinguish between cause and effect.


  • Japanese have the highest life expectancy of all earth's inhabitants. This does not mean that you live longer or healthier, once you have the Japanese nationality or living in Japan. It also can not conclude that the Japanese lifestyle and eating style that promotes health or other life - styles and dietary habits are detrimental to health. Also, a genetic component is conceivable, for example, by islanders a lower genetic mixing subject as mainland residents.
  • Citizens who are between age 20 and 50 years of age or a mentally intellectually challenging activity, sick less often from Alzheimer 's disease. This is the fact on the Correlatio level. The interesting question is now: Cancels Alzheimer's disease from even in youth time and prevents the inclusion of a mentally demanding activity or
  • Prevented a mentally demanding activity Alzheimer's disease?

Bradford -Hill criteria for causality in medicine

Austin Bradford Hill, a British statistician and epidemiologist - who pointed the way with Richard Doll was the first of a link between smoking and lung cancer (so-called British Doctors Study) - postulated the following nine maxims by which or a suspected cause - effect relationship in medicine. epidemiology should be checked:

These criteria were in 1965 in The Environment and Disease: Association or Causation? forth - this publication is still one of the most cited scientific works. Sir Austin Bradford Hill, however, has refused to use these nine points as rigid rules - but this list is often misunderstood and downright taught as a "checklist ". According to Hill, these maxims should but serve causalities postulated to critically think.

Hill has in the same publication, the blind faith in significance tests criticized because such tests probably can exclude a random error, but no systematic and methodical error - but just etiological / epidemiological studies run the risk of suffering from the latter. Similarly, within the meaning of economists Hill proof of a causal relationship is not enough to have measures in the interest of public health. Cost - benefit analyzes in all affected individuals were necessary; because the sheer increase in life expectancy can harm the quality of life among other things - for example, the waiver of a beloved hobby that brings an increased accident risk. These measures should be carried out without statistically watertight solid causality evidence at negligible cost and relatively large expected utility.

See also Phillips & Goodman ( 2004): The missed lessons of Sir Austin Bradford Hill on a review of the original work of 1965 and its significance for the epidemiology and medical etiology.