Olsen J
Int J Epidemiol. 1984 Sep;13(3):347-50. doi: 10.1093/ije/13.3.347.
The frequency of induced abortions varies greatly between and within populations, and the currently employed measures of the ratio of spontaneous abortions are distorted proportionally to the number of induced abortions. Corrections are therefore often necessary to avoid bias when risk ratios for spontaneous abortions are estimated. The potential magnitudes and direction of the bias associated with such risk ratios (under the null hypothesis) are given under certain model assumptions. Adjustment of the estimated risk ratios using an appropriate model for the given data is proposed, rather than using a fixed correction factor.
人工流产的发生率在不同人群之间和人群内部差异很大，目前所采用的自然流产率的衡量指标会随着人工流产数量成比例地扭曲。因此，在估计自然流产的风险比时，为避免偏差，通常需要进行校正。在某些模型假设下，给出了与这些风险比（在零假设下）相关的偏差的潜在大小和方向。建议针对给定数据使用适当的模型来调整估计的风险比，而不是使用固定的校正因子。
