Department of Epidemiology, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
Modeling of Noncommunicable Diseases Research Center, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
Epidemiol Health. 2020;42:e2020024. doi: 10.4178/epih.e2020024. Epub 2020 Apr 9.
Although several causal models relevant to epidemiology have been proposed, a key question that has remained unanswered is why some people at high-risk for a particular disease do not develop the disease while some people at low-risk do develop it. The equivalence model, proposed herein, addresses this dilemma. The equivalence model provides a graphical description of the overall effect of risk and protective factors at the individual level. Risk factors facilitate the occurrence of the outcome (the development of disease), whereas protective factors inhibit that occurrence. The equivalence model explains how the overall effect relates to the occurrence of the outcome. When a balance exists between risk and protective factors, neither can overcome the other; therefore, the outcome will not occur. Similarly, the outcome will not occur when the units of the risk factor(s) are less than or equal to the units of the protective factor(s). In contrast, the outcome will occur when the units of the risk factor(s) are greater than the units of the protective factor(s). This model can be used to describe, in simple terms, causal inferences in complex situations with multiple known and unknown risk and protective factors. It can also justify how people with a low level of exposure to one or more risk factor(s) may be affected by a certain disease while others with a higher level of exposure to the same risk factor(s) may remain unaffected.
尽管已经提出了几种与流行病学相关的因果模型，但一个悬而未决的关键问题是，为什么一些处于特定疾病高风险的人没有患上这种疾病，而一些处于低风险的人却患上了这种疾病。本文提出的等效模型解决了这一难题。该模型提供了一种个体水平上风险和保护因素总体效应的图形描述。风险因素促进了结果（疾病的发生）的发生，而保护因素则抑制了这种发生。等效模型解释了总体效应如何与结果的发生相关。当风险和保护因素之间存在平衡时，两者都无法克服对方；因此，结果不会发生。同样，当风险因素的单位数小于或等于保护因素的单位数时，结果也不会发生。相反，当风险因素的单位数大于保护因素的单位数时，结果就会发生。该模型可以用于以简单的术语描述具有多个已知和未知风险和保护因素的复杂情况下的因果推断。它还可以解释为什么暴露于一个或多个风险因素水平较低的人可能会受到某种疾病的影响，而暴露于相同风险因素水平较高的其他人可能不会受到影响。
