Wulff H R
Medical Department C, Herlev University Hospital, Denmark.
Scand J Gastroenterol Suppl. 1988;147:7-10. doi: 10.3109/00365528809099152.
The limitations of conventional group comparative therapeutic trials are discussed. They include: the heterogeneity problem (due to biological variations within the sample) and the extrapolation problem (i.e. the problem of external validity). These problems may to some extent be overcome by multiple cross-over studies in a single patients. Such studies may be useful in selected cases in daily clinical work, but could also be used for detecting treatment effects in rare diseases. Usually, it is necessary to measure the clinical effect by means of clinical scores, for which reason ranking methods must be used. The statistical significance may be judged by means of a permutation test. The risk of committing a type II error in single patient studies is usually high.
讨论了传统组间比较治疗试验的局限性。这些局限性包括：异质性问题（由于样本内的生物学差异）和外推问题（即外部效度问题）。在单个患者中进行多次交叉研究可以在一定程度上克服这些问题。此类研究在日常临床工作的特定病例中可能有用，但也可用于检测罕见病的治疗效果。通常，有必要通过临床评分来衡量临床效果，因此必须使用排序方法。可通过置换检验判断统计学显著性。在单患者研究中犯II类错误的风险通常很高。
