Part 1 - Cancer and risk factors



Part 1 - Cancer and risk factors

Read the following and answer the questions that follow.

Something that increases the chance of disease is called a risk factor. Thus, data show that a higher proportion of women who do not have children suffer from breast cancer than women who do have children, but this does not mean that having no children causes breast cancer.

Looking for links between risk factors and disease is called epidemiology. Finding links between risk factors and disease can be difficult because different aspects of a person’s lifestyle interact. To see if there is a link between obesity and cancer, you might think that cancer rates in people with a healthy body weight could be compared with rates in people who are obese. However, physical inactivity, unhealthy diets, heavy smoking and genetic predisposition to cancer may be more common among obese people, and it might be one of these and not obesity that is causing cancer.

If an epidemiologist thinks he or she has found a link (this would be his or her hypothesis) it must then be tested. Studies need to be repeated using large samples and on several independent occasions to see if the same results are found. If lots of studies support the hypothesis it is more likely to be accurate.

The likelihood of the studies’ findings being genuine and not due to chance must also be assessed. Statistical tests assess the probability of the findings being due to chance. Generally, if this is less than 5 per cent, the findings are considered to be ‘significant’.

If the findings are not due to chance and are significant then they can be submitted to a reputable journal where the editor will commission other experts to check the findings (this is called peer review) before publishing them.

Having discovered the link it then becomes necessary to understand the biology behind the link. For example, the links between smoking and lung cancer have been proven in hundreds of studies since the 1950s and it has now been shown how certain chemicals in cigarettes can damage DNA, and how this damage can lead to cancer.

Questions

1. What is a risk factor?

2. Why is finding links between a risk factor and a disease difficult?

3. What makes the link between a risk factor and a disease more accurate and, therefore, more reliable?

4. When are findings statistically significant?

5. What should you check before believing claims by companies that their product is beneficial or by journalists that a product is harmful?

Part 2 - Early epidemiology

Read the material below on one of the first epidemiological studies and answer the questions that follow.

On 1 September 1854, cholera broke out in central London and within ten days 500 people had died of it. John Snow recorded the site of each death on a map. Among the victims were both poor and wealthy.

At a time when cholera was thought to be spread by inhaling infected air, Snow suspected that it might be caused by contaminated water. There were a number of water pumps in the locality and the data led Snow to identify a suspect pump.

Questions

1. What two factors was John Snow attempting to correlate?

6. To gauge from the map, which pump did John Snow suspect?

7. How could John Snow test his hypothesis that a water pump was the sole risk factor increasing the likelihood of catching cholera?

8. If cholera was an air-borne disease, how might the distribution of cases on the map above appear?

9. What other risk factor did John Snow eliminate?

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