Department of Environmental Health, National Institute for Health and Welfare, P.O. Box 95, 70701 Kuopio, Finland.
Eur J Epidemiol. 2012 Apr;27(4):281-6. doi: 10.1007/s10654-012-9649-y.
There is a need to better define phenotypes of asthma. However, many studies have data available only on asthma and atopy, so they are often used to define ‘atopic’ and ‘non-atopic’ asthma. We discuss and illustrate the problems of analyzing such outcomes. We used the 31 year follow-up of the Northern Finland Birth Cohort 1966 (n=5,429). ‘Atopic asthma’ and ‘non-atopic asthma’ were defined based on presence or absence of atopy (any skin prick test ≥3 mm) at age 31. Gender and ownership of cat in childhood were used as risk factors. Simple calculations on hypothetical datasets were used to support the conclusions. ‘Atopic asthma’ and ‘non-atopic asthma’, are not well separated disease entities. The association of a risk factor with ‘atopic asthma’ and ‘non-atopic asthma’ is determined both by its association with asthma and with atopy. E.g. if a risk factor is not associated with asthma, but is protective for atopy, this will produce a protective association with ‘atopic asthma’, but an opposite association with ‘non-atopic asthma’. This is the result from the typical analysis, which uses all non-asthmatics as the comparison group. Valid results, unconfounded by atopy, can be gained by comparing asthmatics to nonasthmatics separately among atopics and non-atopics, i.e. by doing the analysis stratified by atopy. If data only on asthma and atopy are available, asthma and atopy should be analyzed at first as separate outcomes. If atopic and nonatopic asthma are used as additional outcomes, valid results can be gained by stratifying the analysis by atopy.
需要更好地定义哮喘的表型。然而，许多研究仅提供有关哮喘和过敏的数据，因此常常用它们来定义“过敏型”和“非过敏型”哮喘。我们讨论并说明了分析此类结果的问题。我们使用了 1966 年芬兰北部出生队列的 31 年随访数据（n=5429）。“过敏型哮喘”和“非过敏型哮喘”是基于 31 岁时是否存在过敏（任何皮肤点刺试验≥3mm）来定义的。性别和儿童时期是否养猫被用作风险因素。使用假设数据集的简单计算来支持结论。“过敏型哮喘”和“非过敏型哮喘”并不是很好区分的疾病实体。风险因素与“过敏型哮喘”和“非过敏型哮喘”的关联取决于它与哮喘和过敏的关联。例如，如果一个风险因素与哮喘无关，但对过敏有保护作用，这将与“过敏型哮喘”产生保护关联，但与“非过敏型哮喘”产生相反的关联。这是典型分析的结果，它使用所有非哮喘患者作为对照组。通过在过敏者和非过敏者中分别将哮喘患者与非哮喘患者进行比较（即通过分层分析进行分析），可以获得不受过敏影响的有效结果。如果仅提供有关哮喘和过敏的数据，则应首先将哮喘和过敏作为单独的结果进行分析。如果将过敏型和非过敏型哮喘作为附加结果使用，则可以通过分层分析来获得有效结果。
