Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Department of Epidemiology and Biostatistics, School of Public Health, University of Zambia, Lusaka, Zambia.
Int J Gynaecol Obstet. 2023 Mar;160(3):842-849. doi: 10.1002/ijgo.14372. Epub 2022 Aug 11.
To illustrate the difference between exposure effects and population attributable effects.
We examined the effect of mid-pregnancy short cervical length (<25 mm) on preterm birth using data from a prospective cohort of pregnant women in Lusaka, Zambia. Preterm birth was live birth or stillbirth before 37 weeks of pregnancy. For estimation, we used multivariable regression and parametric g-computation.
Among 1409 women included in the analysis, short cervix was rare (2.4%); 13.6% of births were preterm. Exposure effect estimates were large (marginal risk ratio 2.86, 95% confidence interval [CI] 1.80-4.54), indicating that the preterm birth risk was substantially higher among women with a short cervix compared with women without a short cervix. However, the population attributable effect estimates were close to the null (risk ratio 1.06, 95% CI 1.02-1.10), indicating that an intervention to counteract the impact of short cervix on preterm birth would have minimal effect on the population risk of preterm birth.
Although authors often refer to "the" effect, there are actually different types of effects, as we have illustrated here. In planning research, it is important to consider which effect to estimate to ensure that the estimate aligns with the research objective.
说明暴露效应与人群归因效应的区别。
我们利用赞比亚卢萨卡一项前瞻性孕妇队列的数据，研究了妊娠中期宫颈管短（<25mm）对早产的影响。早产是指妊娠 37 周前的活产或死产。为了进行估计，我们使用了多变量回归和参数 g 计算。
在纳入分析的 1409 名女性中，宫颈管短的情况较为罕见（2.4%）；13.6%的分娩为早产。暴露效应估计值较大（边际风险比 2.86，95%置信区间[CI] 1.80-4.54），表明与无宫颈管短的女性相比，宫颈管短的女性早产风险显著升高。然而，人群归因效应估计值接近零（风险比 1.06，95%CI 1.02-1.10），表明针对宫颈管短对早产影响的干预措施对早产的人群风险影响极小。
尽管作者经常提到“某种”效应，但实际上存在不同类型的效应，正如我们在这里所说明的。在规划研究时，重要的是要考虑估计哪种效应，以确保估计值与研究目标一致。
