Bergk Verena, Gasse Christiane, Schnell Rainer, Haefeli Walter E
Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Germany.
Swiss Med Wkly. 2005 Apr 2;135(13-14):189-91. doi: 10.4414/smw.2005.10893.
Due to low response rates mail surveys have been called into question as research instruments in general practice. The most effective actions to reduce non-response, such as financial incentives and complex follow-up procedures, are costly. We investigated whether a good response rate is achievable with a less costly survey design, and examined the effect of increased response rates due to repeated follow-ups on survey results.
In a mail survey on drug interactions among 2000 general practitioners in south-west Germany, most well-known criteria influencing response rates were met except financial incentives. A four stage design with two reminders was applied and the time course of response was recorded. Results after both reminders were calculated with 95% confidence intervals and compared with initial results using the Jonckheere-Terpstra test with correction for multiple testing. A p <0.01 was considered significant.
Although we did not provide financial incentives we achieved a response rate of 60.8% with our survey design. The first reminder with a simple postcard was almost three times less effective than the second reminder including another copy of the questionnaire. For only two survey questions, the answers of late respondents differed significantly from those of initial respondents (p <0.01). For these two questions, cumulative results after both reminders never differed from initial results by more than 3.7%.
Even if financial incentives are not affordable, good response rates can be obtained among general practitioners when surveys are meticulously planned and implemented. Potential non-response bias introduced by those general practitioners who do not answer despite numerous reminders, cannot be tested by comparing early and late respondents. Therefore, we suggest that the impact of reminders on survey results should be assessed early. If no bias can be detected one further reminder with a copy of the questionnaire might result in estimates very similar to those after numerous reminders.
由于回复率较低，邮件调查作为全科医疗中的研究工具受到了质疑。降低无回复率的最有效措施，如经济激励和复杂的跟进程序，成本很高。我们调查了采用成本较低的调查设计是否能实现较高的回复率，并研究了多次跟进导致的回复率提高对调查结果的影响。
在一项针对德国西南部2000名全科医生的药物相互作用邮件调查中，除经济激励外，满足了影响回复率的大多数知名标准。采用了包含两次提醒的四阶段设计，并记录了回复的时间进程。计算两次提醒后的结果及其95%置信区间，并使用Jonckheere-Terpstra检验并校正多重检验，将其与初始结果进行比较。p<0.01被认为具有统计学意义。
尽管我们没有提供经济激励，但我们的调查设计仍实现了60.8%的回复率。用简单明信片发出的第一次提醒效果几乎不到包含问卷另一份副本的第二次提醒的三分之一。只有两个调查问题，后期回复者的答案与初始回复者的答案有显著差异（p<0.01）。对于这两个问题，两次提醒后的累积结果与初始结果的差异从未超过3.7%。
即使无法提供经济激励，精心策划和实施调查时，在全科医生中也能获得较高的回复率。尽管多次提醒仍不回复的全科医生所引入的潜在无回复偏差，无法通过比较早期和后期回复者来检验。因此，我们建议应尽早评估提醒对调查结果的影响。如果未检测到偏差，再用问卷副本进行一次提醒可能会得到与多次提醒后非常相似的估计结果。
