Meta 分析的统计学基础(北京大学)

Meta-分析的统计学基础王洪源 北京大学公共卫生学院 流行病学与卫生统计学系 why_w@

一、 概

述

什么是循证医学 Evidence-based medicine (EBM) 循证医学是在对个体病人制定临床 决策时应基于当前最佳的科学研究 成果。

循证医学是最佳的证据、临床经验 和病人价值的有机结合。

用X线进行乳腺癌筛查 Mammography for breast cancer is an established screening method Is screening with mammography justifiable? Gotzsche & Olsen [Nordic Cochrane Centre] conducted a systematic review in 2000 and updated it in 2001. They identified 8 large RCTs on this topic, with over 182,000 women randomized

The authors found that no trial data were of high quality– Two were of medium quality, and the rest were poor quality or flawed.

When the results of the two medium quality trials were combined, the risk ratio was 1.00 (95% CI 0.96, 1.05)

They concluded that “screening for breast cancer with mammography is unjustified”

The US Preventive Services Task Force reviewed the same set of trialsRecently, a 2001 Cochrane Collaboration review of the same trials concluded that

six of the eight trials were "flawed" or of "poor quality" and that the pooled results from the remaining two better trials did not support a benefit from mammography.

The meta-analysis performed for the USPSTF on the most current published data found that the pooled effect size of the combined trials was sizable and statistically significant: the summary relative risk (RR) of breast cancer death among women randomized to screening in seven trials that included women older than 50 was 0.77 (95 percent CI, 0.67-0.89).

The USPSTF recommends screening mammography, with or without clinical breast examination, every 1-2 years for women aged 40 and older.

被动吸烟的危害 A topic of great debate and controversy for many years First few epidemiologic studies were published in 1918

Hackshaw et al. conducted a very comprehensive systematic review in 1997 They identified 37 published studies that reported risk of lung cancer among lifelong non-smoking women according to the husband’s smoking status

Their meta-analysis revealed that the overall risk of lung cancer among lifelong non-smoking women was 1.24 times higher when their husbands smoked, as compared to those women whose husbands did not smoke.

什么是循证医学利用发表的文献证据解决临床问 题对证据进行严格分级,提供指导对医 学文献评价分级的实践指南,并充分考 虑病人的需求和意愿解决具体临床问 题。 但这绝非否认从古至今传统决策 中亦在部分使用上述方法。

循证方法的两个关键方面 证据应从最强(如随机试验及随 机试验的系统评价)到最弱(如: 运用生理学指标且非系统的临床 观察)分级。 医疗决策仅靠证据远远不够

,还 须考虑病人的价值取向和意愿。

循证医学证据的分级 一级：所有 RCT 的系统评价 /Meta- 分析。 二级：单个样本量足够大的RCT。 三级：设有对照组但未用随机方法分组的 研究。 四级：无对照的系列病例观察。 五级: 专家意见。

系统性综述 Systematic reviews(系统评价) 是循证医学重要的手段。 是根据某一具体的临床问题，采用系统、 明确的方法收集、选择和评估相关的临 床原始研究，筛选出合格者并从中提取 和分析数据，为疾病的诊治提供科学的 依据。

循证医学与传统医疗实践的四 个重要区别(1992 JAMA) 系统收集的证据优于非系统的临床观察 以病人终点结局为判效指标的试验优于 仅根据生理学原理制定指标的试验 解释医学文献对医生是一项重要技能,有 必要正规学习一些证据的相关通则,以达 到熟练解释的程度 医生对病人的个体化评价优于专家意见。

Meta - analysis 是在系统性综述时为了合并多个独立的 研究结果，所使用的统计方法。 可以将针对同一问题的，多个独立的研 究结果进行定量分析。 目前，国外文献常常将系统评价与Meta分析交叉使用。 All systematic reviews are not metaanalyses!

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