Topic 10.5
Key Concepts
- Reproduction Number: The average number of cases caused by one infected person.
- Incidence: The likelihood of a disease occurring in a population over a specific period.
- Immunity Threshold: The percentage of a population that needs immunity to stop disease transmission.
- Vaccination Paradox: The appearance of equal sickness in vaccinated and unvaccinated groups when vaccination rates are high.
- Relative Risk: The ratio of the likelihood of an outcome occurring in an exposed group compared to an unexposed group.
Summary
In this topic, we’ve seen how statistics guide public health efforts to combat disease. By using concepts like reproduction numbers, incidence rates, and relative risk, experts can predict outbreaks, protect at-risk populations, and save lives. From cholera in the 1800s to COVID-19 today, data remains a powerful tool in the fight against infectious diseases.
Extension Activities
You are an epidemiologist living in London in the 1950s. You have noticed an increase in lung cancer patients presenting to hospitals in London.
There have also been recent weather events that resulted in heavy smog.
On your way to work, you notice advertising in which doctors and dentists are endorsing new brands of cigarettes (almost everyone smokes these days) and begin to wonder whether the pollution is causing the increase in lung cancer deaths or whether it could be smoking (or both).
(Of course, we now know smoking causes cancer and is extremely unhealthy!)
You undertake a study to investigate lung cancer (Professor Richard Peto has also been a key researcher in this area)
You send a questionnaire to all the lung cancer patients in the hospitals in the city, asking questions about where they usually live (to find out if they are exposed to pollution through living in the city or not) and their smoking habits.
You send the same questionnaire to a control group of non-cancer patients who were matched to the age and gender of the cancer group.
The results of your study are in the 2×2 table below:
|
Disease group (all living in the city and exposed to smog) |
Number of smokers (exposed) |
Number of non-smokers (not exposed) |
TOTAL |
|
Lung cancer patients |
647 |
2 |
649 |
|
Non-cancer patients |
322 |
27 |
349 |
|
TOTAL |
969 |
29 |
998 |
Calculate the relative risk of lung cancer for smokers, compared to non-smokers
Relative Risk = Incidence of lung cancer in exposed ÷ Incidence of lung cancer in unexposed
Click to reveal the answer!
Answer: (647÷969) ÷ (2÷29) = 0.6677 ÷ 0.0689 = 9.96, i.e. smokers were about 10 times more likely to get lung cancer than non-smokers.