Tennant A, Badley E M
ARC Epidemiology Research Unit, University of Manchester, United Kingdom.
J Epidemiol Community Health. 1991 Mar;45(1):81-5. doi: 10.1136/jech.45.1.81.
The aim was to develop an alternative method of investigating non-response bias in postal surveys, including a method of calculating a final full (100%) coverage confidence interval which avoids the wide intervals of existing approaches.
As part of a two stage survey of disablement in the community, a first phase postal questionnaire was sent to 25,168 households in Calderdale, West Yorkshire, England. Confidence intervals were calculated to investigate the precision of estimates using a "no bias" model, where the prevalence in non-responders is assumed to be the same as in responders.
A total of 21,889 postal questionnaires were returned (87%), representing households containing 42,826 people aged 16 years and over. This was achieved by the original post (1st wave, 57% response); two further postal follow ups (2nd and 3rd waves, taking the response to 73% and 81% respectively), the latter including a small personal call back; and a final postal follow up (the 4th wave).
The cumulative estimated prevalence of those with dependence was plotted as the survey progressed. The final wave full coverage estimated prevalence for those aged 16-64 years was 12.8 per 1000 with 95% confidence intervals of 11.3-14.4 per 1000. The integrity of this estimate holds as long as the true prevalence in non-responders is within the calculated non-response confidence interval under the no bias assumption, 9.7-16.0 per 1000 people. This latter interval represents the tolerance of prevalence in non-responders implied by the no bias assumption.
The findings have general implications for monitoring non-response bias in postal screening questionnaires. The confidence interval approach developed in this paper offers an alternative to existing regression based estimates, giving an indication of the range of prevalence amongst non-responders that could be tolerated before the no bias assumption used by the model is breached. It is suggested that this approach can be used to determine both the extent of bias, and to aid decision making about the appropriate juncture to terminate follow up. It highlights the potential, particularly in the context of a computerised survey operation, of methodological investigation occurring simultaneously with survey operation.
旨在开发一种调查邮寄调查问卷中无应答偏倚的替代方法，包括一种计算最终完全（100%）覆盖置信区间的方法，该方法可避免现有方法中出现的宽区间。
作为社区残疾两阶段调查的一部分，向英格兰西约克郡卡尔德代尔的25168户家庭发送了第一阶段的邮政问卷。使用“无偏倚”模型计算置信区间，以调查估计值的精度，该模型假定无应答者的患病率与应答者相同。
共返回21889份邮政问卷（87%），代表包含42826名16岁及以上人群的家庭。这是通过原始邮寄（第一波，57%的应答率）、两次进一步的邮政随访（第二波和第三波，应答率分别达到73%和81%）实现的，后者包括一次小型的个人回访；以及最后一次邮政随访（第四波）。
随着调查的进行，绘制了依赖者的累积估计患病率。16 - 64岁人群在最后一波的完全覆盖估计患病率为每1000人中有12.8人，95%置信区间为每1000人中有11.3 - 14.4人。只要在无偏倚假设下，无应答者的真实患病率在计算出的无应答置信区间内（每1000人中有9.7 - 16.0人），该估计的完整性就成立。后一个区间代表了无偏倚假设所隐含的无应答者患病率的容忍度。
这些发现对监测邮寄筛查问卷中的无应答偏倚具有普遍意义。本文开发的置信区间方法为现有的基于回归的估计提供了一种替代方法，给出了在模型使用的无偏倚假设被打破之前，无应答者中患病率可容忍范围的指示。建议该方法可用于确定偏倚程度，并有助于在适当的时候做出终止随访的决策。它凸显了方法学研究与调查操作同时进行的潜力，特别是在计算机化调查操作的背景下。
