Original Article
Telephone interviews can be used to collect follow-up data subsequent to no response to postal questionnaires in clinical trials

https://doi.org/10.1016/j.jclinepi.2011.04.011Get rights and content

Abstract

Objective

Follow-up data were collected using postal questionnaires and if participants did not respond, then data was collected using telephone interviews. The objectives of this study were to examine, for the two methods, how respondents differed in characteristics and whether the observed treatment difference varied.

Study Design and Setting

A large clinical trial of lower back pain.

Results

About 60% (98/163) of the nonresponders to postal questionnaire provided data by telephone, which increased the overall response rate by 14% (from 71% to 85%). A consistent treatment difference was found across the methods for the outcome measures at 12 months, implying that the observed treatment effect had not been modified. There were some differences between the participants: responders of postal questionnaire were older, likely to be female, white (ethnic origin), not working, with less disability of back pain, compared with those who responded by a telephone interview. At 12 months, there was greater improvement in back pain, disability, and general health for those who responded by postal questionnaires.

Conclusion

Researchers should consider the use of more than one method of collecting data as this increases response rate, participant representativeness, and enhances precision of effect estimates.

Introduction

What is new?

Key findings?

  1. The key findings in this study were that participants who responded to postal questionnaire differed in some of their demographic characteristics and baseline outcomes compared with those who responded by telephone interviews. These differences may be a potential source of bias, which occur because the methods of data collection differ in their implementation. However, if any degree of bias was present, this was consistent across the treatment arms. The implication of this was that an overall treatment difference for an outcome could be obtained irrespective of the way the data have been collected.

What this adds to what was known?
  1. In clinical trials, where the comparison of interventions is of focal interest, follow-up data are often collected using a single method, for example, postal questionnaires. In this article, we have illustrated that collecting data on respondents of postal questionnaires supplemented with collecting data on nonrespondents by telephone can increase response and increase generalizability.

What is the implication, what should change now?
  1. The implication of this article is: telephone interviews should be considered as an effective way in reducing loss to follow-up of participants in clinical trials; researchers should consider additional methods of collecting data from participants who are not responding to initial requests. However, if different methods are used to collect data in a clinical trial, then the data need to be carefully scrutinized for any biases and how these may affect the overall estimate of treatment effect.

Several methods for collecting follow-up data from participants who take part in research studies have been cited in the literature and these include the use of the postal questionnaires, face-to-face interviews, telephone interviews, and use of the Internet [1], [2], [3]. The postal questionnaire is the most frequently used and is considered to be the most cost effective but is often associated with the lowest response rate [4]. Poor response to questionnaires is known to reduce the statistical power of the study as the “effective” sample size is reduced. It can also introduce bias if the nonresponders are systematically different on outcomes of interest to those who respond to the questionnaires.

Much of the literature focuses on assessing ways of improving response to postal questionnaires at follow-up (e.g., giving incentives, use of shorter questionnaires, or use of reminders by telephone to return questionnaires) [5], [6]. The use of an additional method, such as a telephone interview, as a means of collecting follow-up data from mailed nonresponders has been reported in a limited number of social and health surveys [7], [8], [9], [10]. However, there are no studies that report the use of two or more methods of collecting follow-up data in a randomized clinical trial setting, where the comparison of interventions or treatments is of focal interest.

This observational study uses data obtained from a large clinical trial of back pain—the Back Skills Training Trial (BeST) [11]—where participants were randomized to one of two complex interventions. The use of the postal questionnaire was the primary method of data collection at follow-up, and if participants had not responded to mailed questionnaires, then attempts were made to capture data on a shorter version of the paper clinical forms through telephone interviews.

The primary aim of this article was to assess whether the estimated intervention effects differed for the two methods of data collection: postal questionnaires or telephone interviews, which were subsequently documented on paper questionnaires. A secondary aim was to explore how those who responded to the follow-up postal questionnaire differed to those who responded to a telephone interview. For both these aims, the following were evaluated: (1) demography and baseline outcomes; (2) response rates; (3) missing data; (4) internal consistency of each outcome, and (5) the 12 month outcome measures.

Section snippets

Design and participants

The BeST [11], [12] was a two-armed pragmatic multicentered randomized controlled trial. The main aim of this trial was to estimate the clinical effectiveness of two complex interventions: active management (AM) vs. AM plus a cognitive behavioral approach (CBA) (AM + CBA) for subacute and chronic low back pain. AM is the standard intervention for back pain and consists of an advice session supplemented by the Back Book [13]. The CBA intervention details a cognitive-based program, which covers

Response rates at follow-up

In total, 701 participants were randomized into the BeST trial, with 233 participants randomized to AM and 468 to AM + CBA (Fig. 1). This was the total planned sample size for this clinical trial. All randomized participants completed a baseline clinical record form providing some or all of their baseline data. Follow-up data at 12 months was available for 85.4% (598/701) of all patients randomized. The total response rate to the postal questionnaire at 12 months was 71.3% (n = 500). Of the

Discussion

The total sample size for the BeST trial of 701 participants took account of 25% loss to follow-up. However, despite this, it is recognized that some of the analyses presented are underpowered, particularly the test of the interaction terms in the regression models. Thus, the significant interaction between treatment and method for missing items should be interpreted with caution. Also, when comparing the two methods of data collection, it is advisable to place less emphasis on the P-values and

Conclusion

We recommend the use of telephone follow-up to collect outcome data from nonresponders in clinical trials. This study has illustrated the importance of the use of two different methods of data collection in reducing loss to follow-up and thus retaining the power of the study. This in turn has yielded data of comparable quality and enhanced precision of effect estimates. One of the most important criteria for a successful clinical trial is retention of patients and their data. Many clinical

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