Definitions of Risk - PDF Document

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  1. Definitions of Risk Brian A. Burt, B.D.S., M.P.H., Ph.D. Abstract: Risk-related terms such as risk factor, modifiable risk factor, demographic risk factor, risk indicator, determinant, and risk marker are often not well defined in the literature. This short report supports the use of a 1996 definition of risk factor, as probably the most commonly used term related to risk, for the Consensus Development Conference on Diagnosis and Manage- ment of Dental Caries Throughout Life, March 26-28, 2001. Dr. Burt is Professor, Department of Epidemiology at the University of Michigan’s School of Public Health. Direct correspon- dence to him at Department of Epidemiology, School of Public Health, University of Michigan, 109 Observatory Street, Ann Arbor, MI 48109-2029; 734-764-5478 phone; 734-764-3192 fax; Reprints will not be available. R press the probability that a particular outcome will occur following a particular exposure.1 There are very few conditions that constitute a sufficient cause in chronic and infectious disease (a sufficient cause be- ing one where a specific exposure will always result in a particular outcome). If there were, it would not be necessary to deal with risk, which often deals with vary- ing degrees of necessary cause (a necessary cause be- ing an exposure that must always precede a particular outcome), though it can also deal with exposures that are neither necessary nor sufficient causes.2 This brief report is to support the uniform use of a previously stated definition of a risk factor in an effort to stan- dardize terminology for this conference. There is general agreement that the term risk fac- tor means an exposure that is statistically related in some way to an outcome, e.g., smoking is a risk factor for periodontitis. But beyond that broad generality is little agreement. There is uncertainty in the literature on whether a risk factor should be truly causal, i.e., a link in the etiological chain, or whether it can be more pe- ripherally associated with an outcome. There also is uncertainty about what strength of association is needed for an issue to be called a risk factor for a disease and just how directly it needs to be associated with the out- come. Also, there is disagreement over whether a risk factor is immutable, like race or gender, or whether it is something that can be modified, i.e., a smoking habit. In the ongoing studies to determine if periodontitis is a risk factor for cardiovascular disease, for example, it is already clear that there is a measure of association be- tween the two factors. However, it is also evident that periodontitis is neither a necessary nor sufficient con- dition for cardiovascular disease, and it remains to be demonstrated whether periodontitis interacts with other conditions to lead to cardiovascular disease, or whether it is a marker for other conditions that may be causal, Key words: risk factor, risk indicator, risk marker, determinant isk is the probability that an event will occur. In epidemiology, it is most often used to ex- i.e., people with periodontitis are also likely to exhibit other factors that may be more directly linked with the outcome of heart disease. Epidemiology is a relatively new science, so per- haps it is not surprising that there is uncertainty in our use of terms. The literature on measures of risk is re- plete with terms of uncertain definition, and suppos- edly standard terms are used in variable ways by differ- ent authors.3 Even the use of a supposedly standard term like risk factor is far from uniform. Rarely does an au- thor define how the term is being used, and the evi- dence upon which a risk factor is identified is often unclear. The term comes with a cluster of related terms like risk indicator, modifiable risk factor, risk marker, determinant, and demographic risk factor, which are often used more-or-less interchangeably. This sort of uncertainty means that the reader has to make up his or her mind what the author has in mind, and that is clearly unsatisfactory. Turning to the standard dictionary for epidemi- ology, we find that uncertainty persists. In Last’s Dic- tionary of Epidemiology, a risk factor (a term only in use since the 1960s) is defined as: an aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or in- herited characteristic which on the basis of epidemiological evidence is known to be as- sociated with health-related condition(s) con- sidered important to prevent.1 That is a broad and rather loose definition that leaves unanswered the issues of causal role, strength of association, and modifiability. The definition then goes on to list the several different meanings that have been ascribed to the term risk factor: • Risk marker: an attribute or exposure that is associ- ated with increased probability of disease, but is not necessarily a causal factor. • Determinant: an attribute or exposure that increases October 2001 ■ Journal of Dental Education 1007

  2. the probability of occurrence of disease or other specified outcome. • Modifiable risk factor: a determinant that can be modified by intervention, thereby reducing the prob- ability of disease. Last agrees that the term risk factor is rather loosely used, and I think we would agree that these defi- nitions still leave important issues unanswered. In an effort to clarify this area, Beck has listed a definition4 that was adopted for the World Workshop on Periodon- tics in 1996: Any definition of risk factor must clearly estab- lish that the exposure has occurred before the outcome, or before the conditions are established that make the outcome likely. This in turn means that longitudinal studies are necessary to demonstrate risk factors. How- ever, there are many situations in biomedicine, and cer- tainly in dentistry, where this has not been done, and indeed where it is unlikely that longitudinal studies ever will be done. In these circumstances, an exposure that is associated with an outcome only in cross-sectional data is called a risk indicator. A risk indicator may be a probable, or putative, risk factor, but the cross-sectional data upon which it is based is weaker than the results of longitudinal studies. This is because the temporal asso- ciation usually cannot be specified from cross-sectional data. Risk factor: an environmental, behavioral, or biologic factor confirmed by temporal se- quence, usually in longitudinal studies, which if present directly increases the probability of a disease occurring, and if absent or removed reduces the probability. Risk factors are part of the causal chain, or expose the host to the causal chain. Once disease occurs, removal of a risk factor may not result in a cure. REFERENCES 1. Last JM, ed. A dictionary of epidemiology. 4th ed. New York: Oxford University Press, 2001. 2. Susser M. Causal thinking in the health sciences. New York: Oxford University Press, 1973:41-7. 3. Burt BA. Risk factors, risk markers, and risk indicators [editorial]. Community Dent Oral Epidemiol 1998;26:219. 4. Beck JD. Risk revisited. Community Dent Oral Epidemiol 1998;26:220-5. This definition is longer than that given by Last, but is “tighter” and more specific. The key contribu- tions from this definition are: a) the emphasis on the the temporal sequence of exposure before outcome; b) the acceptance that a risk factor is part of the causal chain; and c) the acceptance that risk factors are in- volved in disease onset, not necessarily in its future progression or resolution. Journal of Dental Education ■ Volume 65, No. 10 1008