Here is why epidemiology is important for HSC Biology

Epidemiology studies how infectious and non-infectious diseases spread. It focuses on understanding how, where and why a disease is spreading. This is valuable as it allows us to predict the cause of outbreaks, allowing us to step the spread of disease. This can save lives and you have likely seen this first hand with the covid-19 pandemic.

The HSC biology course assesses epidemiology in the context of data analyses questions. Typically, you will be presented a data such as a graph which shows the number of people smoking and another graph of the number of new lung cancer diagnosis. This is epidemiology since you can correlate the increase in smokers increased the number of people getting lung cancer.

Table of contents


Epidemiology bathtub illustrating the effect of incidence, mortality rate and recovery rate on diseases prevalence.
Understanding the epidemiology bathtub

Prevalence is the number of people who have the disease, this is influenced by:

Recovery rate is the rate people are getting better.

Incidence is the number of people who have recently acquired the disease.

Mortality rate is the rate people are dying from the disease

  • An increase in the mortality rate, lowers the prevalence of the disease.
  • An increase in the recovery rate, lowers the prevalence of the disease.
  • A reduction in the incidence rate, lowers the prevalence of the disease

Epidemiologist often use this language in order to communicate to one another. For the HSC it is important that you have a solid grasp of this language as it is often what differentiates higher order responses.

The three major types of epidemiology:

Descriptive, analytical and experimental epidemiology.

Descriptive epidemiology is about understanding who, what, when, where, causes, risk factors and modes of description. This is through looking at data of outbreaks, identifying its limitations and eccentricities. These studies require a Sherlock Holmes like investigation. The nature and patterns of the spread allows the epidemiologists to design public health measures to save lives and prevent the outbreak from growing.

Analytical epidemiology deals with the search for cause and effect, or why and how. This is through considering:

  • Demographic factors such as age, race, and gender.
  • Constitutional factors such as blood type and immune status.
  • Actions or acts such as sun exposure and smoking.
  • Circumstances such as living near a toxic waste disposal site or being exposed to carcinogens.

Epidemiologists use analytical epidemiology to quantify exposure-outcome relationships and test hypotheses about causality.

Experimental epidemiology is the study of the relationships between various factors that determine disease incidence and prevalence in communities. Experimental epidemiology includes randomized controlled trials (often used for new drugs and drug testing), field studies (conducted on individuals at high risk of developing disease), and community studies (socially induced there are three case types for the study of disease This method uses prospective population studies designed to test epidemiological hypotheses, usually attempting to relate postulated causes to observed outcomes.

It has been said that epidemiology alone cannot prove that a particular exposure caused a particular outcome. However, it can correlate the two, we will get to more of this in our case studies.

Understanding disease spread

Having lived through a pandemic, you probably know best the power of epidemiology. During the COVID global health emergency, we watched as the disease started at epidemic level before being increased to a pademic status and once it stabilised in the community it was then considered an endemic. But what do these terms actually mean?

An epidemic is an unexpected increase in the number of cases of disease in a particular geographical area. This can be an increase from a normal number of cases or an increase from no prior cases.

A pandemic when disease growth becomes exponential. This means that the rate of increase is skyrocketing, with more cases each day than the day before. When a virus is declared a pandemic, it has nothing to do with virology, herd immunity, or the severity of the disease.

An endemic, is when the incidence of the disease is no longer changing.

Case study 1

Smoking and lung cancer

Smoking can’t be said to cause cancer. Full stop. How crazy is that! There have been endless debates over this and court cases. But there is such a strong evidence which correlates smoking and lung cancer. For that reason we can say don’t smoke because it increases your risks of developing lung cancer. And that is the power of epidemiology. To save lives.

Eoidemiology uses past data looking at the number of people smoking and the incidence in lung cancer. These studies found that when people smoke more, the number of lung cancer cases increases.

From here public education campaigns such as the “stop smoking” advert can educate and change public behaviour. Deterring people people from smoking cost money. However, the long term financial saving in not needing to treat future patients is worth it.

Case study 2

Sun exposure and melanoma incidence

Another epidemiology study motivated the “slip, slop, slap” campaigns you have likely seen. Link sunburn to the incidence of melanoma made it clear that melanoma and sunburn are correlated. Uv radiation causes our skin cells to accumulate mutatutions. Eventually, these healthy cells with mutations become cancerous.

So check out the graph below and see if you can identify when the slip slop slap campaigns began to change individuals sun safety behaviour.

What this means for you.

Epidemiology is an active field of research. Since the covid-19 outbreak, the number of researches


Question 1.

From the 2018 HSC Biology Question 24

Question 2.

Evaluate the social, cultural and economic effects of an epidemiology study of your choosing [6 marks]

Previous chapter: Homeostasis

Next chapter: Prevention of disease

Return to Open Access Biology HSC Textbook Overview

Learning Summary.

  • Epidemiology terminology: incidence, prevalence, recovery rate and mortality
  • Three types of epidemiology studies: descriptive, analytical, experimental
  • Smoking is correlated with lung cancer
  • Sun exposure is correlated with skin cancer


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