Vineis P
Imperial College London, Department of Epidemiology and Public Health, Norfolk Place, London W2 1PG, UK.
J Epidemiol Community Health. 2008 Mar;62(3):273-8. doi: 10.1136/jech.2007.063644.
In this paper I wish to introduce some ideas about scientific reasoning that have reached the epidemiological community only marginally. They have to do with how we classify things (diseases), and how we formulate hypotheses (causes). According to a simplified and currently untenable model, we come to defining what a disease, or a protone or a chromosome, is by progressive simplification--that is, by extracting an essence from the individual characters of disease. At the end of this inductive process a single element, which guarantees the unequivocal inclusion in the category, is identified. This is what has been called "Merkmal-definition" (Merkmal meaning distinctive sign)--that is, the definition of disease would be allowed by the isolation of a crucial property, a necessary and sufficient condition, which makes that disease unique (and a chair out of a chair, a proton out of a proton, etc). However many objections have been raised by Wittgenstein, Eleanor Rosch and others to this idea: a Merkmal is not always identifiable, and more often a word is used to indicate not a homogeneous and unequivocal set of observations, but a confused constellation with blurred borders. This constellation has been called a fuzzy set and is at the basis of the semantic theory of metaphors proposed by MacCormac and the prototype theory proposed by Rosch. In this way the concept of disease, for example, abandons monothetic definitions, amenable to a necessary and sufficient characteristic, to become "polythetic." I explain how these concepts can help medicine and epidemiology to clarify some open issues in the definition of disease and the identification of causes, through examples taken from oncology, psychiatry, cardiology and infectious diseases. The definition of a malignant tumour, for example, seems to correspond to the concept of "family resemblance," since there is no single criterion that allows us to define unequivocally the concept of cancer: not morphology (there are borderline situations between benign and malignant), not clinical features, not biochemical or molecular lesions. In the case of schizophrenia, the problem of indetermination, as it has been defined, is even stronger. Mental disease probably cannot be distinguished from health in a clearcut way (according to a minimum set of necessary criteria), but it would have a fuzzy border with mental conditions that characterise normal subjects, through intermediate linking conditions.
在本文中，我想介绍一些关于科学推理的观点，这些观点在流行病学领域中只是略有涉及。它们与我们如何对事物（疾病）进行分类以及如何形成假设（病因）有关。根据一个简化且目前难以成立的模型，我们通过逐步简化来定义一种疾病、一个质子或一条染色体是什么——也就是说，从疾病的各个特征中提取出本质。在这个归纳过程结束时，会确定一个单一元素，它能保证明确无误地归入该类别。这就是所谓的“特征定义”（“Merkmal”意为独特标志）——也就是说，疾病的定义可以通过分离出一个关键属性，一个必要且充分的条件来实现，这个条件使该疾病独一无二（椅子中的椅子、质子中的质子等等）。然而，维特根斯坦、埃莉诺·罗施等人对这一观点提出了许多反对意见：特征并非总是可识别的，而且一个词通常并非用于表示一组同质且明确无误的观察结果，而是表示一个边界模糊的混乱集合。这个集合被称为模糊集，是麦科马克提出的隐喻语义理论和罗施提出的原型理论的基础。例如，疾病的概念就这样摒弃了适合必要且充分特征的单一定义，而变得“多特征”。我通过从肿瘤学、精神病学、心脏病学和传染病中选取的例子，解释这些概念如何有助于医学和流行病学澄清疾病定义和病因识别中的一些未解决问题。例如，恶性肿瘤的定义似乎符合“家族相似性”的概念，因为没有单一标准能让我们明确无误地定义癌症概念：不是形态学（良性和恶性之间存在临界情况），不是临床特征，不是生化或分子病变。在精神分裂症的情况下，不确定性问题，正如所定义的那样，甚至更严重。精神疾病可能无法以明确的方式（根据一组最少的必要标准）与健康区分开来，但它会通过中间的连接条件与表征正常受试者的精神状态有一个模糊的边界。
