Epidemiology is the study of health across large groups of people, i.e. the health of populations.

It sounds a dry area and doesn't get a lot of attention, but it's a rich source of information and a fertile starting ground for many areas of research.

For example, there have been low levels of asthma in most of Africa compared to the industrialised world. This is changing as industrialisation occurs. There’s much to learn from the difference in rates of asthma between countries and continents - why does asthma increase with industrialisation?

Whiplash is another fascinating area for epidemiological study.

Based on the research available, whiplash varies enormously according to jurisdictional policies.

Whiplash is mainly a problem for motor vehicle accident compensation systems (as well as the individuals suffering with the problem!) and provides a fascinating insight into how treatment approaches and legal influences sway the development and prolongation of some health problems.

The contrast between Australian jurisdictional policies is not commonly discussed. When talking to claims managers in different states, they are often surprised to hear there are differences.

In 1986 in Victoria, the Transport Accident Commission was formed. The old organisation was known as the Motor Accidents Board. A series of legislative changes were introduced:

• No fault insurance was introduced;
• The person involved in a car accident was required to pay the first $450, or so, of medical expenses; and
• A 10% impairment threshold was introduced for lump-sum impairment benefits.

Overnight, the incidence of whiplash claims in Victoria dropped enormously.

In everyday medical practice, peoples' behaviour changed. Prior to the 1986 changes, all medical costs were covered.

People regularly attended their doctor for a check-up post-accident, often with only minor symptoms, and on a number of occasions when they had no symptoms. That is just what people did. And then the doctor, feeling the need to do something, would typically refer for treatment; most commonly physiotherapy.

This situation still applies in some states of Australia.

As a wise Rehabilitation Physician who looked at the claims data once commented, “The caring health professional” then took charge. Regular treatment, often twice or more a week, was instituted. This resulted in an ongoing focus on the sore neck. Medical terms were used and restrictions on activity may have been put in place.

The results were often long-term treatment, activity avoidance and the condition was more likely to be troublesome for a longer period.

Post-1986 there was a threshold for medical expenses. People questioned the value of paying out for a consultation, as they do in normal life when purchasing any service. Is there value in this?

In most cases where the condition was minor, they were disinclined to go to the doctor. Very sensible; less referrals was associated with less long-term problems.

Did this mean people were free from neck pain? No, they experienced the problem, but didn't become part of a system that inadvertently caused them to restrict activities.

Oversimplifying the situation, you say?

A few months ago I saw a 26 year old who'd been involved in a distressing but otherwise uncomplicated rear end collision in Perth. Following the usual course, her general practitioner referred her to a physiotherapist. Along with frequent passive treatment, she was told that she had to stop her previous exercise of going to the gym on a regular basis and jogging.

Shockingly, she was also told her neck was too weak to be subjected even walking as a form of exercise.

That’s a dramatic example, but people are regularly advised to avoid activities because of whiplash. "Don’t lift, stop your Taekwondo, your neck’s not ready for going to the gym. "

In contrast, an enormous number of guidelines and evidence based reviews tell us to tell our patients they are best to continue normal activities.

Researchers have looked at issue in different countries and continents: Canada, Europe, and to a lesser extent, Australia. Research tells us that as well as psychosocial factors, the type of policy / legislation in the state / country influences outcomes.

In countries where studies have been performed, neck pain is common after rear end collisions. However, in countries where there are no compensation mechanisms, the reported problems are significantly less.

Does this mean we should assume people with whiplash have less bother than they are reporting? Not at all.

Everyday behaviour patterns provide a commonsense understanding of why problems occur. If you have lots of time and start to think about it, you're more likely to feel tired than if you’re busy and engaged in what you are doing.

If there is lots of attention to your problem, and you're given all sorts of worrying labels, you're more likely to think about the problem and worry about your future.

And neuroscience tells us nerves involved with pain mechanisms 'learn'. With greater attention to the problem, the nerves hear the signals more easily, and the problem is more likely to become entrenched.

There is more to whiplash than the "system’’, but it does seem to be a significant factor.

Want to read more?

http://www.ncbi.nlm.nih.gov/pubmed/19251076
http://www.ncbi.nlm.nih.gov/pubmed/15687859
http://www.ncbi.nlm.nih.gov/pubmed/18704519