# AME循证杂谈022|诊断准确性研究的样本量计算——基于PASS软件实现

Published at: 2015年第1卷第S1期

【案例】一研究者计划研究超声诊断胆囊结石的准确度，手术探查为金标准，预实验结果见表1，取alpha=0.05，power=90%，双侧检验，总计需要多少样本？

n(Specificity)表示待计算的样本量，按Specificity计算样本量，此处为选择项；power=90%表示把握度为0.9，alpha=0.05表示检验水准为0.05；P ( Prevalence)=0.4，此处应该为先验概率，理论上应该是人群总体的胆囊结石的患病率，本例用样本的胆囊结石的患病率代替先验概率；Se0 (Null Sensitivity)=0.5，Se1 (Alternative Sensitivity)=0.8，Sp0 (Null Specificity)=0.5，Sp1 (Alternative Specificity)=0.6，此处敏感度及特异度基线值设置为0.5，也可以根据实际情况设置为一个更大的数值，一般来说应不小于0.5。

One-Sample Sensitivity and Specificity Power Analysis

Numeric Results for testing H0: Se = Se0 vs. H1: Se ≠ Se0 and H0: Sp = Sp0 vs. H1: Sp ≠ Sp0

Test Statistic: Binomial Test

References

Obuchowski, N.A., Zhou, X.H. 2002. 'Prospective studies of diagnostic test accuracy when disease prevalence is low,' Biostatistics, Volume 3, No. 4, pages 477-492.

Li, J., Fine, J. 2004. 'On sample size for sensitivity and specificity in prospective diagnostic accuracy studies,' Statistics in Medicine, Volume 23, pages 2537-2550.

Machin, D., Campbell, M.J., Tan, S.B., Tan, S.H. 2008. Sample Size Tables for Clinical Studies, Third Edition. Wiley-Blackwell, Chichester, United Kingdom.

Zhou, X.H., Obuchowski, N.A., McClish, D.K. 2002. Statistical Methods in Diagnostic Medicine. Wiley-Interscience, New York.

Report Definitions

Sens. Power is the power of the sensitivity test. It is based on the N1 observations.

Spec. Power is the power of the specificity test. It is based on the N-N1 observations.

N is the total sample size of the study. It is equal to N1 + N2.

Se0 is the sensitivity under H0. The sensitivity is the proportion of diseased subjects that yield a positive test result.

Se1 is the sensitivity under H1. The sensitivity is the proportion of diseased subjects that yield a positive test result.

Sp0 is the specificity under H0. The specificity is the proportion of non-diseased subjects that yield a negative test result.

Sp1 is the specificity under H1. The specificity is the proportion of non-diseased subjects that yield a negative test result.

Target Alpha is the alpha (probability of rejecting H0 when H0 is true) that was desired.

Actual Sens. Alpha is the alpha that was actually achieved by the sensitivity test, calculated from the binomial distribution.

Actual Spec. Alpha is the alpha that was actually achieved by the specificity test, calculated from the binomial distribution.

P is proportion of the population that actually has the condition (disease) of interest, called the prevalence.

Summary Statements

A total sample size of 438 (which includes 175 subjects with the disease) achieves 100% power to detect a change in sensitivity from 0.5 to 0.8 using a two-sided binomial test and 90% power to detect a change in specificity from 0.5 to 0.6 using a two-sided binomial test. The target significance level is 0.05. The actual significance level achieved by the sensitivity test is 0.0491 and achieved by the specificity test is 0.0483. The prevalence of the disease is 0.4.

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doi：10.3978/kysj.2014.1.1462