“Sick individuals and sick populations” is a paper written by Geoffrey Rose in 1985. It was published in the International Journal of Epidemiology and is one of the most influential public health papers ever written.
He describes and compares the ‘high-risk’ and ‘population’ strategies for prevention of disease. I think most readers will be able to access the original paper here, but if you cannot access it, this Wikipedia article gives you the basic idea.
The main idea is that the largest number of cases of ill health happen not in those at high risk, but in those who have just some risk, simply because there are more of them. See below for a more detailed summary.
The distribution of risk in a population often follows a bell curve (see figure), so if you are able to shift the whole curve to the left (lower risk in red), then everybody has a lower risk and you will get a fewer number of cases.
The high risk approach
The ‘high-risk’ approach to prevention is where medical professionals identify people with a condition (e.g. high blood pressure) and prescribe medication to prevent it developing into heart disease, or other diseases high blood pressure might be a risk factor for.
The advantages are that people are likely to be motivated to take the medication and the intervention will be tailored to the individual. The disadvantages are that any fixes may be temporary because the cause of high blood pressure is not identified. Also, predicting new cases of disease (known as incidence) is difficult to predict for individuals.
The population strategy approach
This approach to prevention aims to shift the distribution of a condition, so that fewer numbers of a case may occur. If there are a lot of 30 year olds with low risk, but a few 50 year olds with high risk, then more cases will occur in the 30 year olds, simply because there are more of them.
The advantages are that there is big potential to change the distribution of a risk factor in a whole population (i.e. how many people have low or high risk), and because changes are happening to whole populations, individuals will not have to struggle to change their behaviours in the face of peer-pressure. Disadvantages are that while large changes will be seen at a population level, only small changes will be apparent at an individual level.
The population approach is fundamental to public health and it is a big reason for why I believe making our environments conducive to health (rather than profit) is vital. I outline my thoughts on why I believe we really could change our environment in this blog post. If we are aiming to shift the distribution of risk so that everyone has a lower risk, for me, making the environment we all live in a healthy one is a huge part of achieving this.