- Email: [email protected]
Risk factors — A misleading concept
Public Health The Journal of The Society of Community Medicine (Formerly the Society of Medical Officers of Health Volume 97 Number 5 September 1983
Risk F a c t o r s - A Misleading Concept During the past decade it has become increasingly fashionable to use the term "risk factor". Different authors, however, have used the concept in ways which imply differing meanings. Applied to any measurable characteristic which has a significant corrlation with mortality, irrespective of whether these relationships are causal, risk factors can be used to assess the probability of premature death. Unfortunately, however, this is not the only way in which the concept has been used. Some authors have used the term to imply causal relationships, and interpreted the work of others as though they too implied causality. The failures of trials of drugs which reduce serum lipids, and of the Multiple Risk Factor Intervention trial in the U.S.A. to reduce mortality fromischaemiwheart disease, should cause us to reconsider the hypothesis on which these trials were based. These hypotheses probably arose in part from abuse of the ":risk.fa¢,to¢ '~ ¢oncept.¢ and from ccmfusion between "cause" and "effect". Despite the failure of the North Karelia project to demonstrate improvement in incidence of coronary heart di~easefollow~xlg;a~s~tastantial reduction in so-called risk factors, negative or inconclusive-:restilts':ffom numbers of other s t u d ' s , and evidence that Eskimo's who suffered little ischaemic, heart disease.w-hertZ=liVing on a high fat diet become subject to coronary disease..aftar~ ~tdO~i~, ~n"Amettean diet and lifestyle, few physicians are yet prepared to ~conslder the possibility'that.hy.perlipidaemia may be an effect rather than a cause of a~ther.0ma.'. Ilastead tl~re~is:~t::~teridencytb" devise elaborate theories to explain away such embarrassing ~;6dings. The alternative view that refined-sugar consumption over a period of years may be the principal dietary factor is a simpler and more elegant explanation which merits re-examination. In other fields too the concept of the "risk factor" is being used and abused. In Sheffield the use of factors associated with sudden infant death has enabled the authority to provide special health-visitor supervision of families where high risk has been predicted. A reduction in incidence of cot death has been attributed to this intervention. The reduction in incidence of cot death, however, has not been confined to Sheffield, but was shared by the whole of Trent region. It may well owe more to the increased popularity of breast feeding combined with the phasing-out of high solute artificial feeds than to selective supervision. In this instance the concept may or may not have conferred benefit, and a longer trial is needed. As the Black report so vividly showed, there is a close relationship between poverty and many indices of poor health. Money would not necessarily correct the health deficiencies of social classes 4 and 5. Their improvement will require identification and correction of the causal factors, which may be only very indirectly associated with income. Furthermore, since chronic ill health is a cause of downward slippage whereas good health increases the chance of climbing the social ladder, some parts of the social-class gradient may be inevitable. Much confused thinking and waste of effort might be avoided if the term "risk factor" were eschewed, and a clear distinction drawn between "predictive factors" and "causal factors".
Risk F a c t o r s - A Misleading Concept During the past decade it has become increasingly fashionable to use the term "risk factor". Different authors, however, have used the concept in ways which imply differing meanings. Applied to any measurable characteristic which has a significant corrlation with mortality, irrespective of whether these relationships are causal, risk factors can be used to assess the probability of premature death. Unfortunately, however, this is not the only way in which the concept has been used. Some authors have used the term to imply causal relationships, and interpreted the work of others as though they too implied causality. The failures of trials of drugs which reduce serum lipids, and of the Multiple Risk Factor Intervention trial in the U.S.A. to reduce mortality fromischaemiwheart disease, should cause us to reconsider the hypothesis on which these trials were based. These hypotheses probably arose in part from abuse of the ":risk.fa¢,to¢ '~ ¢oncept.¢ and from ccmfusion between "cause" and "effect". Despite the failure of the North Karelia project to demonstrate improvement in incidence of coronary heart di~easefollow~xlg;a~s~tastantial reduction in so-called risk factors, negative or inconclusive-:restilts':ffom numbers of other s t u d ' s , and evidence that Eskimo's who suffered little ischaemic, heart disease.w-hertZ=liVing on a high fat diet become subject to coronary disease..aftar~ ~tdO~i~, ~n"Amettean diet and lifestyle, few physicians are yet prepared to ~conslder the possibility'that.hy.perlipidaemia may be an effect rather than a cause of a~ther.0ma.'. Ilastead tl~re~is:~t::~teridencytb" devise elaborate theories to explain away such embarrassing ~;6dings. The alternative view that refined-sugar consumption over a period of years may be the principal dietary factor is a simpler and more elegant explanation which merits re-examination. In other fields too the concept of the "risk factor" is being used and abused. In Sheffield the use of factors associated with sudden infant death has enabled the authority to provide special health-visitor supervision of families where high risk has been predicted. A reduction in incidence of cot death has been attributed to this intervention. The reduction in incidence of cot death, however, has not been confined to Sheffield, but was shared by the whole of Trent region. It may well owe more to the increased popularity of breast feeding combined with the phasing-out of high solute artificial feeds than to selective supervision. In this instance the concept may or may not have conferred benefit, and a longer trial is needed. As the Black report so vividly showed, there is a close relationship between poverty and many indices of poor health. Money would not necessarily correct the health deficiencies of social classes 4 and 5. Their improvement will require identification and correction of the causal factors, which may be only very indirectly associated with income. Furthermore, since chronic ill health is a cause of downward slippage whereas good health increases the chance of climbing the social ladder, some parts of the social-class gradient may be inevitable. Much confused thinking and waste of effort might be avoided if the term "risk factor" were eschewed, and a clear distinction drawn between "predictive factors" and "causal factors".