Trussell J, Rodríguez G, Ellertson C
Office of Population Research, Princeton University, NJ 08544, USA.
Contraception. 1998 Jun;57(6):363-9. doi: 10.1016/s0010-7824(98)00042-0.
The purpose of this study was to provide new estimates of the effectiveness of the Yuzpe method of emergency contraception and to offer correctly computed estimates of the confidence intervals for estimated effectiveness rates. Through a literature search, seven studies that present the number of women treated and outcome of treatment by cycle day of unprotected intercourse relative to expected day of ovulation were identified. Probabilities of conception by cycle day of intercourse among women not using contraception and the associated variance-covariance matrix from five other datasets were estimated, and these external estimates were used to assess the effectiveness of the Yuzpe regimen. The 40 estimates of effectiveness, based on seven separate studies and the seven studies combined and five different sets of conception probabilities by cycle day, ranged from a low of 44.2% to a high of 88.7%. The preferred point estimate is that emergency contraceptive pills reduce the risk of pregnancy by 75.4%, with a 95% confidence interval extending from 65.6% to 82.4%. True effectiveness is likely to be at least 75% because treatment failures (observed pregnancies) include women who were already pregnant when treated and women who became pregnant after being treated.
本研究的目的是提供对尤兹佩紧急避孕法有效性的新估计，并给出估计有效率的置信区间的正确计算值。通过文献检索，确定了七项研究，这些研究呈现了接受治疗的女性数量以及相对于预期排卵日按未采取保护措施性交的周期日划分的治疗结果。估计了未使用避孕措施的女性按性交周期日的受孕概率以及来自其他五个数据集的相关方差 - 协方差矩阵，并使用这些外部估计值来评估尤兹佩方案的有效性。基于七项单独研究、七项研究合并以及按周期日划分的五组不同受孕概率得出的40个有效性估计值，范围从低至44.2%到高至88.7%。首选的点估计值是紧急避孕药将怀孕风险降低75.4%，95%置信区间从65.6%延伸至82.4%。实际有效性可能至少为75%，因为治疗失败（观察到的怀孕情况）包括治疗时已怀孕的女性以及治疗后怀孕的女性。
