– Epidemiology: the science dealing with the transmission and control of disease.
– Features of an epidemiological study that help prove the cause of disease:
Through analysis of statistics, it must demonstrate a significant link between the cause and the disease
There has to be a chronological order of events; that is, the cause must come before the disease
The study must be done on a large range of subjects, in terms of age, sex, race, occupation, socioeconomic status, and geographical position
The results should persist over time
The cause-and-effect relationship should be independent of other factors
The study should be repeatable by other investigators at different time, and different places¸ using different methods.
– The epidemiological studies concerning lung cancer are a good example – the studies range over many decades, starting from the 1950s, when levels of lung cancer first began to become noticeable.
– The people surveyed in the studies came from a wide range of ages, from WWI veterans who had started smoking because they were given free cigarettes to the wave of women who had begun to take up smoking in the 1970s.
– The studies have shown that there is a strong correlation between smoking and lung cancer.
– Lung cancer is the uncontrolled growth of tumors in the lungs.
– Causes:
Tobacco smoke contains over 4000 chemicals, many carcinogenic (causing cancer) such as:
Benzene: found in petrol fumes
Tar: road surfacing
Arsenic: rat poisening
Methanol: rocket fuel
– Effect:
As the tumour grows, the air sacs in the lungs are destroyed and breathing becomes difficult. The lungs collapse and abscess and the patient may begin coughing up blood. The cancer can metastasise (spread) to other vital organs and cause death.
– Statistical Information:
Mass production of cigarettes began in 1880 – free cigarettes were given to WWI soldiers
In the 1930s there was a sudden lung cancer epidemic
The first epidemiological studies which showed a relationship between smoking and lung cancer were in the 1950s, but they did not have conclusive results – they just showed a reduced live expectancy
A 1960 study by Horn in the United states, compared average smokers and non-smokers life expectancy, the smokers had 10 times greater chance of dying.
In 1964 the Surgeon’s General Advisory Committee concluded that cigarette smoking was a cause of lung cancer.
In the 1970s, as the numbers of female smokers began to increase, lung cancer became the number one cause of cancer death.
Studies have shown a correlation between the number of cigarettes smoked each day and the risk of contracting lung cancer at an earlier stage
Also, a gradual decrease in the numbers of people smoking in the past 20 years has been mirrored by a decrease in sufferers of lung cancer
