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Published on 21.05.14 in Vol 16, No 5 (2014): May

Preprints (earlier versions) of this paper are available at, first published Sep 09, 2013.

This paper is in the following e-collection/theme issue:

    Letter to the Editor

    Intervention Adherence is Related to Participant Retention: Implications for Research

    1Centre for Mental Health Research, The Australian National University, Canberra, Australia

    2Centre for Addiction and Mental Health, Toronto, ON, Canada

    Corresponding Author:

    John Alastair Cunningham, PhD

    Centre for Mental Health Research

    The Australian National University

    Building 63

    Canberra, 0200


    Phone: 61 02 6125 1859

    Fax: 61 02 6125 0733


    Two challenging issues in Internet intervention research, as well as in other behavioral intervention trials, are ensuring that participants receive the intervention (adherence) and that their outcomes are captured at follow-up (retention) [1]. The interesting analysis presented by Murray et al [2] demonstrated that, at least in their study sample, the participant adherence and retention were positively related.

    One issue to consider is whether this finding can be replicated in other study samples. It is possible that research involving, for example, different recruitment methods or with higher (or lower) retention rates, might not display this same positive relationship. To that purpose, results were examined from an Internet intervention trial that employed a proactive telephone recruitment method and obtained complete follow-up data for 86% of participants [3-5]. As with the Murray et al study [2], adherence (measured by the number of intervention participants logging onto a brief alcohol intervention, where N=92; 57 participants logged onto the intervention and 35 participants did not log on) and retention were strongly positively related (retention at 3-months: logged onto intervention=100%, did not log on=80%, P<.001; retention at 6-months: logged onto intervention=100%; did not log on=80%, P<.001; retention at 12-months: logged onto intervention=96%; did not log on=74.3%, P=.002; Fisher’s Exact Tests).

    Given that the positive relationship between adherence and retention can be replicated, what are the implications of this finding? From one perspective, the fact that these two key issues are related could underline the increased importance of obtaining a good retention rate. This is because the positive relationship of adherence to retention implies that a confound in the interpretation of the results is more likely as loss to follow-up (or reduced adherence to the intervention) increases. Alternatively, it could be argued that this positive relationship might reduce the importance of obtaining a good retention rate. This is because traditional intent-to-treat analysis assumes that participants who are lost to follow-up do not make any change in their behavior from baseline to follow-up (and are included as imputed values in the analysis based on this assumption). If it is then assumed that only those participants who accessed the intervention will actually make a change in their behavior, then the fact that participants who adhere to the intervention are more likely to follow-up can only increase the likelihood that participants who are lost to follow-up are less likely to have made a change in their behavior (thus validating the intent-to-treat analysis assumption). Determining which of these implications is correct is important, particularly in a field where low retention rates are an unfortunate reality in many research trials [1].

    Conflicts of Interest

    None declared.


    1. Eysenbach G. The law of attrition. J Med Internet Res 2005;7(1):e11 [FREE Full text] [CrossRef] [Medline]
    2. Murray E, White IR, Varagunam M, Godfrey C, Khadjesari Z, McCambridge J. Attrition revisited: adherence and retention in a web-based alcohol trial. J Med Internet Res 2013;15(8):e162 [FREE Full text] [CrossRef] [Medline]
    3. Cunningham JA, Wild TC, Cordingley J, van Mierlo T, Humphreys K. A randomized controlled trial of an internet-based intervention for alcohol abusers. Addiction 2009 Dec;104(12):2023-2032 [FREE Full text] [CrossRef] [Medline]
    4. Cunningham JA, Wild TC, Cordingley J, Van Mierlo T, Humphreys K. Twelve-month follow-up results from a randomized controlled trial of a brief personalized feedback intervention for problem drinkers. Alcohol 2010 Jun;45(3):258-262 [FREE Full text] [CrossRef] [Medline]
    5. Cunningham JA, Wild TC, Humphreys K. Who uses online interventions for problem drinkers? J Subst Abuse Treat 2011 Oct;41(3):261-264 [FREE Full text] [CrossRef] [Medline]

    Edited by G Eysenbach; submitted 09.09.13; peer-reviewed by E Murray, R Kok, S Langrial; accepted 15.05.14; published 21.05.14.

    ©John Alastair Cunningham. Originally published in the Journal of Medical Internet Research (, 21.05.2014.

    This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on, as well as this copyright and license information must be included.