Introduction

Pain is an individual experience, whose subjective nature makes it difficult to define, describe or measure, yet which is common to all human beings. As description and measurement are nonetheless essential, so, therefore, is a definition that suits both patients and professionals. Pain is helpfully, therefore, defined by the International Association for the Study of Pain (IASP) as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described by the patient in terms of such damage’.

Chronic pain is defined by the IASP as ‘pain that persists beyond normal tissue healing time’. A range of factors may be involved, including physical and biological factors, and also behavioural and cognitive factors, and these may dominate the experience of chronic pain, which is ultimately primarily subjective (Box 1.1).

Box 1.1 Acute and Chronic Pain

Acute pain	→ → → → → →	Chronic pain
Physiological		Pathological
Health preserving		Maladaptive
Warns of damage		Dysfunctional healing
Allows evasive action		Abnormal response to injury

What is Chronic Pain?

There are many similarities in the symptoms and impact of chronic pain between most individuals who experience chronic pain, irrespective of its cause. Consequently, there are also many similarities in approaches to preventing or managing chronic pain of different aetiological or diagnostic backgrounds. This has led some to propose the existence of a ‘chronic pain syndrome’, and certainly for many clinical and research purposes, there is considerable merit in regarding chronic pain as a single, global, clinical entity (while also paying suitable attention to individual, treatable causes of chronic pain).

Why is Epidemiology Important?

Epidemiology is ‘the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control health problems’.

(Last RJ. (2001) A Dictionary of Epidemiology, 4th edn. Oxford: International Epidemiological Association.)

It is the latter part of this definition that makes it such an important science in clinical medicine. The last twenty or so years have seen the publication of many good quality epidemiological studies of chronic pain that have enhanced our understanding of its causes, impact and approaches to management. Good epidemiological research on chronic pain can, and does, provide important information on its classification and prevalence and factors associated with its onset and persistence. This can inform the design and targeting of treatment and preventive strategies (Box 1.2).

Box 1.2 How Does Epidemiology Help Us with Chronic Pain?