筛检项目总效果评价的新指标——需筛检人数

Number needed to be screened in a study: a novel measure for disease screening effect

目的介绍需筛检人数(NNBS)的基本概念、计算方法及用途。方法利用需治疗人数(NNT)的基本思想引入评价筛检项目总效果的新指标,以大便隐血试验(FOBT)筛检结直肠癌的随机对照试验和X线检查筛检乳腺癌的随机对照试验的两项研究为实例,计算需邀请参加筛检人数(NNI)和NNBS。结果通过计算得到欲通过实施FOBT筛检方案,要在14年内使当地45-74岁人群预防1例因结直肠癌所致的死亡,NNI为1220人,NNBS为665人;此外,欲通过实施乳腺X线检查筛检方案,要在8年内使当地40-74岁妇女预防1例因乳腺癌所致的死亡,NNI为1961人,NNBS为1494人。结论NNBS能以较直观的方式来评价筛检项目的总效果,便于研究人员、卫生决策者和社会公众进行更好的沟通和交流。

Objective To introduce the concept, methods for calculation and application of ＂number needed to be screened＂ （NNBS） in epidemiologic studies. Methods The concept of ＂number needed to treat＂ （NNT） was extended for disease screening strategies. For the purpose of illustration, the values of number needed to invite for screening （NNI） and number needed to be screened （NNBS） were calculated on the basis of the results from two randomized controlled screening trials -- Nottingham randomized controlled trial of faecal-occult-blood screening for colorectal cancer and Swedish mammographic screening trial for breast cancer in two counties. Results In order to prevent one death from the colorectal cancer among local people aged from 45 to 74 during the 14 years of follow-up, the NNI and NNBS for faecal- occult-blood screening program were 1220 and 665, respectively. In addition, in order to prevent one death from breast cancer among local women aged 40-74 during 8 years of follow-up, the NNI and NNBS for mammographic screening program were 1961 and 1494, respectively. Conclusion Compared with the traditional indices, NNBS can evaluate the overall effectiveness of a screening program in an intuitively understandable manner so as to facilitate the communication among medical researchers, health workers, health policy makers and the public.