Carneiro António Vaz
Centro de Estudos de Medicina Baseada na Evidência, Faculdade de Medicina de Lisboa, Lisboa, Portugal.
Rev Port Cardiol. 2003 Nov;22(11):1393-401.
The choice of randomized controlled trials as the best evidence on therapeutic (or preventive) measures is based on the fact that this design is the only one that allows the establishment of causality, i.e. a relationship between an intervention and an outcome. For example, it is essential for the cardiologist treating patients with congestive heart failure (CHF) from systolic dysfunction of the left ventricle to know if the use of selective beta-blockers will reduce mortality. In order to find this out, he must have access to the published evidence on beta-blockers use in CHF, either through primary sources--RCTs--or secondary sources--systematic reviews. The results from clinical trials must be presented in a standardized way: in RCTs, authors usually present proportions (or rates, or percentages) of events (acute myocardial infarction, stroke, death) in each study group: experimental and control. These events are usually dichotomous, i.e. they are either present or not. In this paper, we will discuss the meaning as well as the interpretation of a number of measures of association in RCTs: absolute risk and absolute risk reduction, relative risk and relative risk reduction, odds ratios, number needed to treat and number needed to harm.
选择随机对照试验作为治疗（或预防）措施的最佳证据，是基于这样一个事实：这种设计是唯一能够确立因果关系的设计，即干预与结果之间的关系。例如，对于治疗因左心室收缩功能不全导致的充血性心力衰竭（CHF）患者的心脏病专家来说，了解使用选择性β受体阻滞剂是否会降低死亡率至关重要。为了弄清楚这一点，他必须能够获取关于β受体阻滞剂用于CHF的已发表证据，要么通过原始资料——随机对照试验，要么通过二手资料——系统评价。临床试验的结果必须以标准化的方式呈现：在随机对照试验中，作者通常会呈现每个研究组（实验组和对照组）中事件（急性心肌梗死、中风、死亡）的比例（或发生率、或百分比）。这些事件通常是二分的，即要么发生要么未发生。在本文中，我们将讨论随机对照试验中一些关联度量的含义及解释：绝对风险和绝对风险降低、相对风险和相对风险降低、比值比、治疗所需人数和伤害所需人数。
