Improving between-wave mailings on longitudinal surveys: A randomised experiment on the UK Millennium Cohort Study


  • Lisa Calderwood Institute of Education



longitudinal, tracking, nonresponse, attrition, survey methods, between-wave mailing, covering letters, advance letters


Typically, longitudinal survey managers send ‘keep in touch’ mailings to sample members between waves to help minimise non-response through failure to locate individuals at future waves. This paper reports the results from a randomised experiment to improve the effectiveness of the between-wave mailing on the Millennium Cohort Study (MCS), a large-scale birth cohort study in the UK. Our experimental intervention, which involved revising the content of the covering letters used in the 2010 mailing, aimed to increase the proportion of sample members responding to the mailing, particularly among those with higher attrition rates i.e. lower educated sample members and minority ethnic groups. The re-design involved making the letter easier to read, due to a concern that poor literacy or English may be a barrier to returning the form for some groups, and changing the style and signatory, motivated by the psychological concepts of reciprocity, linking and helping tendencies. Our main finding, that the design of the covering letter has a minimal impact on the effectiveness of these mailings, will help guide further research in this area and help to inform practice on longitudinal surveys. The results also make an important contribution to the existing evidence on the content of advance letters more generally and thereby have broader applicability for survey research and practice.

Author Biography

Lisa Calderwood, Institute of Education

Lisa leads the teams responsible for survey management and cohort maintenance on the Millennium Cohort Study, the 1970 British Cohort Study and the 1958 British Cohort Study (National Child Development Study). She has extensive experience and expertise in all aspects of survey design and is able to offer consultancy in this area. Her research interests are in survey methodology, particularly in relation to longitudinal survey design and implementation.




How to Cite

Calderwood, L. (2014). Improving between-wave mailings on longitudinal surveys: A randomised experiment on the UK Millennium Cohort Study. Survey Research Methods, 8(2), 99–108.




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