Effects and Paradoxes of Risk Competition
Purpose: Analysis of effects of risk competition for preparation of recommendations concerning the true account of this competition in risk assessments and use of their results. Material and methods: Effects of risk competition between different independent risk sources are demonstrated and analyzed applying theoretical formulas and risk calculation examples. In some practically important cases, these effects can have a paradoxical character. Competition can also take place between dependent risk sources (e.g., a biological dependence like synergism or antagonism). In this case, it is necessary to take into account the relationship between age specific risk coefficients for dependent harmful impacts. Morbidity risk can be also the object of risk competition. Results and conclusions: Due to risk competition the simple summing of lifetime risk indices is inadmissible. Summing up such indices is possible with controlled inaccuracy in case of their smallness only. It is demonstrated analytically and via the calculation example. Only age specific risk coefficients and standardized mortality (morbidity) indices possess the additivity feature. Analysis of risk competition and features of the lifetime risk indices leads to conclusion that these indices should be carefully used in any risk assessments and in application of their results. True accounting of the competition in risk assessment is controlled by the total survival function. As to epidemiological studies, obtaining of their results in the form of age specific mortality coefficients allows to prevent possible negative effects of risk competition. Lifetime risk indices - objects of the risk competition - should be used with cautiousness in different risk assessments and applications of their results.