Epidemiology

Note to students:

Read the relevant module notes, textbook and other sources before starting each Module Exercise to ensure that your answer shows an integrated knowledge of the topic and is based on the epidemiological method using relevant terminology. Carrying out this preliminary work is essential to meeting the assessment expectations for Epidemiology.

Sometimes you will need to read forward in the notes to other modules to answer a question, as you would when using a textbook. When you have developed a rough plan for the answer, refine your work by reading relevant publications and journal articles which add to substance. All answers must be referenced, although parts of answers involving calculations may have fewer references than written parts.

The Learning Guide contains essential information on answering questions and submitting work. If you have reached this stage without reading it or understanding the contents you should backtrack now and read it to assist you in meeting the assessment expectations.

MODULE EXERCISE 1: The development of epidemiology

Through hard work John Snow rose from poverty to became a doctor, pioneering the use of anaesthetics in childbirth which he succesfully applied to Queen Victoria’s later births. He developed analytical epidemiology as a hobby, which enabled effective control of London’s catastrophic cholera outbreak at a time when Pasteur’s microbial germ theory of disease was still unknown. Since computer availability, Epidemiology has become a cutting edge modern science, yet its originas are older than those of Microbiology

Background to the exercise:

You are asked to read parts of John Snow’s original report which is presented in the module notes, chapter 1 to give you background to the roots of epidemiology and show how it developed from the outset not merely as a method of controlling communicable disease, but as an analytical approach for the identification of a broad range of health “risk factors” (please note that the term “risk factors” may be misleading in that they can be both beneficial [eg: hours of exercise per day] and detrimental [eg: total intake of saturated fats].

The exercise:

Part 1: After reading Snow’s report, and consulting other sources, identify and briefly discuss the risk factors under which cholera is most likely to spread, classifying them under a number of sub-headings relevant to epidemiology.

Part 2: Visit three internet sites of international or local health agencies (eg: organisations, associations or government departments) and write brief notes on each agency’s epidemiological activities, based on the definition of epidemiology in Porta’s 2014 Dictionary of Epidemiology (the most recent, reliable definition in 2020) as set out in the module notes.

Aims of the exercise:

1. To introduce students to the evaluation of epidemiological reports in terms of their principal components, and to encourage students to understand and identify risk factors.
2. To orientate students to the nature of epidemiology and the relevant role played by selected health and other agencies.

Hints:

1. Risk factors fall into categories such as environmental, lifestyle, demographic, etc.
2. Communicable disease control (CDC) is only one aspect of an epidemiologist’s work.
3. When reading the question, write down any words you don’t understand and look them up. Clarifying even one word can demystify an entire question!

MODULE EXERCISE 2: Public health (large area) epidemiology

Background to the exercise:

The Australian Government Department of Health (DOH) operates the National Notifiable Diseases Surveillance System (NNDSS) which receives notifications (written reports) from medical practitioners and institutions (eg: hospitals) of newly-occurring “notifiable” (state and territory gazetted) disease cases. These data are sorted, collated and published by the DOH in table form, both as absolute numbers and as rates per unit population (in epidemiology, always try to use rates which enable comparison of disease occurrence between different places and times).

These data are extremely useful for those who wish to monitor changes of disease incidence (see definition) with time or with place, and relating these to environmental, lifestyle, demographic and other risk factors which can then be controlled to reduce disease incidence and epidemics.

While these annual data facilitate large-scale epidemiology, they are also available at a higher level of resolution (more detail) for specific months, places, population groups, age and sex.

The exercise:

Part 1: Using the internet, access a NNDSS table showing rates for Chlamydial infection, a sexually transmissible infection, for the past 15 years for all of Australia.

Then produce a fully-labelled, computer-generated, time trend graph for this disease, using Excel®

Part 2: Briefly discuss three possible reasons why the rate for this disease might have changed over the past 15 years. Do not base this on common knowledge, press reports or magazine articles which are invariably sensationalistic and incorrect, but on information in the scientific literature, giving references in an epidemiologically acceptable format, as shown in the Learning Guide. Here a Scopus search will pay dividends, while Google Scholar referencing is rarely complete.

Aims of the exercise:

1. To acquire skills in the extraction, presentation, analysis and use of quantitative information/data from a large-area, epidemiological data base.
2. To develop early perspectives on risk factors for specific diseases, and insight as to why and how these might change with environmental, economic, lifestyle or other changes.

Hints:

1. Use data for the years 2006 to 2020 inclusive (data for 2021 is, as yet, incomplete) for all of Australia.
2. Visit later module notes to learn how to construct graphs meeting all labelling and structural conventions. In other words, “read ahead” in the notes as you would with a book.
3. To answer part 2, first identify risk factors for the disease, then find information from authoritative web sites and reports on how these risk factors might have changed over the past 15 years in Australia. See the learning guide for information on acceptable information sources.
4. Again, it would be best to start off by looking up all unknown words! Do you really know, for example, what “rates” means?

MODULE EXERCISE 3: Bivariate linear regression analysis (correlation)

Background to the exercise:

As Safety, Health and Environmental (SHE) consultant, the occupational health nurse of a large tyre production plant advises you that a large number of workers in the same production area are visiting the clinic each day to receive simple medication for headaches. In some cases the headaches are severe, and some workers believe that their headaches are caused by the high air temperatures during the day which they have reported to their union.

Your environmental investigation shows that temperatures at different sites in the plant are similar, but vary greatly on a day to day basis, suggesting poor ambient temperature control. The nurse supplies a daily record of all headaches of a similar type over the period of a month, as well as details of the number of people employed in the factory each day. The production engineer supplies records of mean production area temperature during each daily shift. These data are tabulated at the end of this question.

The exercise:

Part 1: Plot a graph using a recognised computer application (eg: Excel®) to see if there is a bivariate, linear correlation between the health condition and temperature, as a potential risk factor. Insert a line of best fit and present your graph for assessment with a short comment on your observations based on this graph.

Calculate Pearsons correlation coefficient r (not r²) using Excel’s “insert function” ( fx).

Part 2: Calculate the same coefficient by hand using a suitable formula, data capture table and calculator/mobile phone only. Present the formula, table and the steps of your hand calculation and comment on any differences in the result for Pearsons r, compared to that obtained in part 1.

List five potentially confounding risk factors (ie: those other than temperature) which you would investigate during further assessment.

Aims of the Exercise:

1. To gain an understanding of the use of bivariate linear regression analysis as a fundamental epidemiological analytical tool.
2. To gain a conceptual idea of risk factors and management of an important health condition

Hints:

1. If the question looks foreign and perplexing you probably need to go back to the module notes where the approach is clearly explained, and work through an example.
2. When calculating, it is essential to check your calculations thoroughly. While marks are given mainly for method, they are also awarded for the correct answer (we are aiming for an accurate intervention), and it is relatively easy to obtain 100% with careful checking of your calculation. Time spent checking can therefor lift your overall average result this semester.
3. The first step when working with raw data is to classify (construct a table). When in doubt, tabulate, when numerical problems will immediately become clearer.
4. Use one more decimal place in your calculations than you want to give in your answer.
5. Use the formula in the module notes rather than the one given in text books, which is for statisticians.
6. When studying health states (diseases and fitness) always calculate and use rates, and not absolute numbers. How can you do that here?

vi. Excel® does not do as much as SPSS and Minitab, but is far more user-friendly, and links well with Word®. Most journals also prefer to publish articles prepared with these two programs. Adding the line of best fit in Excel® involves highlighting the graph first by clicking on it, when the menu tab for this function will appear.

Employees with headaches and corresponding mean production area temperature