Link-Gelles Ruth, Westreich Daniel, Aiello Allison E, Shang Nong, Weber David J, Rosen Jennifer B, Motala Tasneem, Mascola Laurene, Eason Jeffery, Scherzinger Karen, Holtzman Corinne, Reingold Arthur L, Barnes Meghan, Petit Susan, Farley Monica M, Harrison Lee H, Zansky Shelley, Thomas Ann, Schaffner William, McGee Lesley, Whitney Cynthia G, Moore Matthew R
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
BMJ Open. 2017 Aug 28;7(8):e017715. doi: 10.1136/bmjopen-2017-017715.
External validity, or generalisability, is the measure of how well results from a study pertain to individuals in the target population. We assessed generalisability, with respect to socioeconomic status, of estimates from a matched case-control study of 13-valent pneumococcal conjugate vaccine effectiveness for the prevention of invasive pneumococcal disease in children in the USA.
Matched case-control study.
Thirteen active surveillance sites for invasive pneumococcal disease in the USA.
Cases were identified from active surveillance and controls were age and zip code matched.
Socioeconomic status was assessed at the individual level via parent interview (for enrolled individuals only) and birth certificate data (for both enrolled and unenrolled individuals) and at the neighbourhood level by geocoding to the census tract (for both enrolled and unenrolled individuals). Prediction models were used to determine if socioeconomic status was associated with enrolment.
We enrolled 54.6% of 1211 eligible cases and found a trend toward enrolled cases being more affluent than unenrolled cases. Enrolled cases were slightly more likely to have private insurance at birth (p=0.08) and have mothers with at least some college education (p<0.01). Enrolled cases also tended to come from more affluent census tracts. Despite these differences, our best predictive model for enrolment yielded a concordance statistic of only 0.703, indicating mediocre predictive value. Variables retained in the final model were assessed for effect measure modification, and none were found to be significant modifiers of vaccine effectiveness.
We conclude that although enrolled cases are somewhat more affluent than unenrolled cases, our estimates are externally valid with respect to socioeconomic status. Our analysis provides evidence that this study design can yield valid estimates and the assessing generalisability of observational data is feasible, even when unenrolled individuals cannot be contacted.
外部效度，即普遍性，是衡量一项研究结果与目标人群中的个体的契合程度的指标。我们评估了一项针对美国儿童13价肺炎球菌结合疫苗预防侵袭性肺炎球菌疾病有效性的匹配病例对照研究中，估计值在社会经济地位方面的普遍性。
匹配病例对照研究。
美国13个侵袭性肺炎球菌疾病的主动监测点。
病例通过主动监测确定，对照按年龄和邮政编码匹配。
通过家长访谈（仅针对已登记个体）和出生证明数据（针对已登记和未登记个体）在个体层面评估社会经济地位，并通过地理编码到普查区在邻里层面评估（针对已登记和未登记个体）。使用预测模型来确定社会经济地位是否与登记有关。
我们纳入了1211例 eligible 病例中的54.6%，发现已登记病例比未登记病例更富裕的趋势。已登记病例在出生时更有可能拥有私人保险（p = 0.08），且母亲至少有一些大学教育程度的可能性更高（p < 0.01）。已登记病例也往往来自更富裕的普查区。尽管存在这些差异，我们用于登记的最佳预测模型的一致性统计量仅为0.703，表明预测价值一般。对最终模型中保留的变量进行了效应测量修正评估，未发现有变量是疫苗有效性的显著修正因素。
我们得出结论，尽管已登记病例比未登记病例在一定程度上更富裕，但我们的估计在社会经济地位方面具有外部效度。我们的分析提供了证据，表明这种研究设计可以产生有效的估计值，并且即使无法联系到未登记个体，评估观察数据的普遍性也是可行的。
