Grimes D A, Snively G R
Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, USA.
Obstet Gynecol. 1999 Jun;93(6):910-4. doi: 10.1016/s0029-7844(98)00567-5.
To assess patients' ability to compare magnitudes of Down syndrome risk at maternal ages of 35 and 40 years, expressed as rates or as proportions.
We used a self-administered, anonymous questionnaire that posed the same comparison in two different formats: 2.6 versus 8.9 per 1000 women (rates) and one in 384 versus one in 112 women (proportions). The study setting included several university-affiliated obstetrics and gynecology outpatient clinics in San Francisco, California. A total of 633 women, whose primary languages were English, Spanish, or Chinese, participated. The main outcome measure was correct identification of the larger of two risks.
Women were more successful with rates (463 of 633 respondents, 73%) than with proportions (353 of 633 respondents, 56%). A paired analysis, in which each woman served as her own control, found risk assessment to be significantly better with rates than with proportions (P < .001). Women with little formal education had difficulty understanding risks framed either way.
The traditional use of proportions to express risk in genetic counseling lacks scientific basis. Rates were easier to understand than proportions, regardless of respondents' age, language, and education.
评估患者比较35岁和40岁孕妇唐氏综合征风险大小的能力，风险以发生率或比例表示。
我们使用了一份自行填写的匿名问卷，该问卷以两种不同形式提出相同的比较：每1000名女性中2.6例与8.9例（发生率），以及384名女性中有1例与112名女性中有1例（比例）。研究地点包括加利福尼亚州旧金山的几家大学附属妇产科门诊诊所。共有633名主要语言为英语、西班牙语或中文的女性参与。主要结局指标是正确识别两种风险中较大的风险。
女性对发生率的识别更成功（633名受访者中有463名，73%），而对比例的识别则较差（633名受访者中有353名，56%）。一项配对分析（其中每位女性作为自己的对照）发现，用发生率进行风险评估明显优于用比例（P <.001）。几乎没有接受过正规教育的女性难以理解以任何一种方式表述的风险。
在遗传咨询中传统使用比例来表示风险缺乏科学依据。无论受访者的年龄、语言和教育程度如何，发生率比比例更容易理解。
