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Improving response rates to postal questionnaires in clinical trials. Rachel Nakash PhD, BSc(Hons), MCSP. Introduction. Patient based outcome measures – assess various aspects of health from patient’s perspective. Usually take format of questionnaire Telephone, face to face, post

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Improving response rates to postal questionnaires in clinical trials

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improving response rates to postal questionnaires in clinical trials

Improving response rates to postal questionnaires in clinical trials

Rachel Nakash

PhD, BSc(Hons), MCSP

  • Patient based outcome measures – assess various aspects of health from patient’s perspective.
  • Usually take format of questionnaire
  • Telephone, face to face, post
  • Post: least expensive, prevents interviewer bias, patient can respond in own time
  • Disadvantages: NON-RESPONSE
non response in a clinical trial
Non-response in a clinical trial
  • Reduces effective sample size, introduces bias
  • What is acceptable loss to follow up?
  • Sackett et al (1997) ‘five and twenty’ rule of thumb
  • Some journals refusing to publish trials with losses > 20%
  • Obtaining losses to follow up < 20% in a clinical trial takes considerable effort
previous research
Previous research
  • Methods of improving response rates to postal questionnaires – mostly SURVEY research
  • No connection to health care
  • Most relevant Cochrane review: Edwards et al (2003): incentives, ‘user friendly’ and shorter questionnaires improve response – but... only 20% of included trials had a health care connection
  • Clinical trial participants ? different to survey participants – lack of literature
phd aims and objectives
PhD aims and objectives
  • 1. Systematic literature review – refinement of previous reviews. Focussed just on health care literature
  • 2. Randomised controlled trial – to test a method of improving response within the context of an existing clinical trial
  • 3. Qualitative study of clinical trial participants
  • 4. Analysis of characteristics of responders and non-responders
setting for the research
Setting for the research
  • Collaborative Ankle Support Trial – CAST
  • A multi centre RCT funded by the NHS HTA
  • Designed to evaluate clinical and cost effectiveness of 3 methods of mechanical support compared to tubigrip in severe ankle sprain
  • Outcomes assessed at 4 weeks, 12 weeks and 9 months following injury using postal questionnaires
CAST pilot phase was used to:
    • Assess response rates
    • Clarify follow up procedures
    • Identify aspects of response to subject to deeper investigation
  • 24 patients recruited onto CAST pilot
A follow up protocol was needed to chase response
  • Developed based on available lit and time and resource constraints of CAST
  • Series of steps involving telephone contacts and repeat mailing of questionnaire
  • Time consuming (?soul destroying!)
  • Response categories developed – summary of how much prompting was required by each patient at each time point
1 systematic literature review
1. Systematic Literature Review
  • Cannot assume methods of improving response in survey research will be successful in clinical trial setting
  • Refinement of previous reviews
  • Limited to ‘health care studies’ on ‘patient populations’
  • More useful and relevant for health researchers using postal questionnaires
    • 13 trials identified evaluating 5 different methods of improving response
    • Questionnaire length, incentives, question order, reminder strategies, information brochure
    • Similar methods of improving response grouped for comparison
    • Random effects model meta-analysis conducted
    • Intense follow up strategies and shorter questionnaires improve response rates
    • The evidence is, however, limited
2 randomised controlled trial
2. Randomised Controlled Trial
  • Method of improving response nested into CAST
  • ‘Trial Calendar’ – a tool to prompt questionnaire return
  • Research question: Does the trial calendar improve response rates and reduce the need for prompting
296 CAST participants randomly allocated to receive a trial calendar or not
  • Effect of calendar assessed using chi-squared test at each follow up point
  • No sig effect on response at any follow up point
  • Logistic regression performed to account for effect of covariates (eg age, sex)
  • Still no effect of trial calendar at any time point (except females with calendar sig better at responding at 9 months – data trawling!)
    • Trial calendar not an effective tool for improving response rates in a clinical trial
    • Follow contact and prompting needs to be high profile and timely – trial calendar too subtle
    • Extra cost involved in implementing a tool such as a trial calendar not justified
3 qualitative study
3. Qualitative Study
  • To gain the participant’s perspective of response issues in clinical trials
  • Semi-structured interviews of a purposive sample of CAST participants
  • 22 participants interviewed – responders and non-responders
  • Framework Analysis used to analyse data (similar to thematic content analysis but deeper).
Common themes:
    • Reasons for response:
      • Personal relevance
      • Agreed to take part – Compliance/trial understanding
      • Obliged to respond – Good service/reciprocation
      • Altruism
      • Important project
    • Reasons for non-response
      • Internal – due to aspects of trial
      • External – beyond control of trial
      • Personal blame – Forgetful, lazy, disorganised…
      • Life events
      • (Full recovery, treatment preference)
    • ‘Happy non-responders’
    • ‘Unhappy non-responders’
    • Serial non-responders – once a non-responder, always a non-responder
  • Conclusions:
    • Recruitment phase very important in appealing to psychological processes of response and ensuring participant fully understands trial follow up
    • ? Convert happy non-responders
4 characteristics of responders and non responders
4. Characteristics of responders and non-responders
  • ? Any predictive characteristics of responders and non-responders
  • Survey researchers have attempted to establish common personal characteristics of responders and non-responders
  • Advantage of a clinical trial is the detailed background information collected at baseline
  • Despite this there is a lack of work looking specifically at CT participants
555 participants recruited onto CAST (not inc pilot)
  • Either responder or non-responder at each follow up point
  • This info combined with CAST database background info to allow for comparisons between responders and non-responders in terms of certain socio-demo characteristics
  • Age, sex, CAST treatment, employment type, education level, recovery
  • Analysis: chi-squared, logistic regression
    • Age the only variable to sig effect response – older people respond better
    • Females generally better at responding
    • Better recovery leads to lower likelihood of response
    • Active refusals to cooperate very low compared to surveys (refusal in a trial usually occurs at recruitment stage)
    • Non-contacts steadily increase at each follow up (incorrect contact details, contact details change, house movers)
overall conclusions and recommendations
Overall conclusions and recommendations
  • Consider carefully and a priori follow up protocols to chase reluctant responders
  • Keep non-response as a result of non-contact to minimum – get as much contact info as possible
  • No evidence incentives effective so don’t bother
  • Careful wording of written/verbal instructions to appeal to theoretical issues of response and understanding of follow up commitment
  • Exclude potential non contacts at baseline
  • Lamb SE, Marsh JL, Hutton JL, Nakash R, Cooke MW; Mechanical supports for acute, severe ankle sprain: a pragmatic, multicentre, randomised controlled trial. Lancet 2009; 373(9663): 575-81.
  • Sackett D, Richardson W, Rosenberg W, Haynes R. Evidence-based medicine: how to practice and teach EBM. New York: Churchill Livingstone 1997.
Groves R, Singer E, Corning A. Leverage-Saliency theory of survey participation. Public Opinion Quarterly. 2000;64:299-308.
  • Edwards P, Roberts I, Clarke M, DiGuiseppi C, Pratap S, Wentz R, et al. Methods to increase response rates to postal questionnaires. The Cochrane Database of Methodological Reviews. 2003(Issue 4):Art. No.: MR000008. DOI: