A word of caution is in order given the controversial subject of this paper. There are two aspects to CFS. The first is an operationally-defined condition, that can be measured and studied. We and other groups are making progress in determining the epidemiology of CFS in primary care using the conventional methods of epidemiological research. However, such research will not shed light on the second problem of CFS. This is the belief, whether self- or doctor-generated, that one is suffering from an illness with that label. Thus, patients are appearing in increasing numbers who believe, often with passion and conviction, that they suffer from chronic fatigue and immune deficiency syndrome (CFIDS) in the USA, or myalgic encephalomyelitis (ME) in the United Kingdom. [...]
As an epidemiologist, I know that a person has CFS only if they fulfil operational criteria. As an observer of the social scene, I also know that ME or CFIDS is defined by the sufferers themselves. Hence, for this paper, a person has ME or CFIDS simply if that is what they believe is wrong with them. Untold confusion has arisen from the failure to distinguish between an operationally-defined epidemiological construct and a social belief system. This essay concerns the latter and not the former.