Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Taking over as the Cochrane Review with the most included studies when it was updated in November 2023, is the Cochrane Methodology Review of strategies to improve the response rates for postal and web questionnaires. Here's lead author, Phil Edwards from the London School of Hygiene and Tropical Medicine in the UK, to outline the importance of the review and its latest findings.

Phil: Postal and web questionnaires are a relatively inexpensive way to collect information from people for research purposes, and it's been estimated that a third of health research studies collect data from participants using a questionnaire. However, if people don't reply to the questionnaire, the research results will tend to be less accurate and less reliable.
Our Cochrane methodology review looks for effective ways to increase response to postal and web questionnaires. We're also planning another Cochrane Methodology Review to find effective methods to increase participation in interviews. 
For the postal and web questionnaires review, we've searched for studies that examined any way to increase response to one of these types of questionnaire in any topic area. The review was first published in 2001 and a vast amount of research was available for this third update, which now includes 758 randomised trials: 670 for postal questionnaires and 88 for electronic questionnaires. These studies include a wide range of people being asked to complete a questionnaire, from patients, doctors, university students, and professors, to marketing managers, accountants, and grocery store managers.
To summarise our results, we found that response will be increased by contacting people before they are sent a questionnaire and that response to postal questionnaires will be increased if they are sent by a university. Response can also be increased by giving an incentive, for example, a small amount of money, or a non‐monetary incentive such as a pen; and may be increased by using a postal questionnaire rather than an web questionnaire, or by providing a choice between a web or a postal questionnaire. Lastly, response can be increased by making questionnaires, letters, and emails more personal, and preferably keeping them short.
To finish with thoughts on costs: some of these ways to increase response require additional materials or administrative time, but some can be implemented at little or no extra cost. For example, researchers may be able to double the odds of response by offering participants a small amount of money for completion of questionnaires or by using recorded delivery, but both could add substantially to costs for large studies. On the other hand, the use of non‐monetary incentives, such as a free pen, may be more affordable, but is likely to be less effective in encouraging response.

Mike: If you would like to read this massive Cochrane review, summarising a large amount of evidence on ways to improve responses rate for postal and web questionnaires, you can find it online at Cochrane Library dot com with a simple search for 'postal and electronic questionnaires'.