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The specific effect of systematic exposure in irritable bowel syndrome: complier average causal effect analysis using growth mixture modeling

Published online by Cambridge University Press:  03 May 2017

H. Hesser*
Affiliation:
Department of Behavioural Sciences and Learning, Linköping University, Linköping, Sweden
E. Hedman
Affiliation:
Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden Department of Clinical Neuroscience, Osher Center for Integrative Medicine, Karolinska Institutet, Stockholm, Sweden
P. Lindfors
Affiliation:
Department of Internal Medicine Sahlgrenska University Hospital, University of Gothenburg, Gothenburg, Sweden Department of Medicine Huddinge, Karolinska Institutet, Stockholm, Sweden
E. Andersson
Affiliation:
Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden
B. Ljótsson
Affiliation:
Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden
*
*Address for correspondence: H. Hesser, Department of Behavioural Sciences and Learning, Linköping University, SE-581 83 Linköping, Sweden. (Email: [email protected])

Abstract

Background

We reanalyzed data from a previously published randomized component study that aimed to test the incremental effect of systematic exposure in an internet-delivered cognitive behavioral treatment (ICBT) for irritable bowel syndrome (IBS).

Methods

Three hundred and nine individuals with IBS were randomly assigned to either the full treatment protocol (experimental condition) or the same treatment protocol without systematic exposure (control). Participants were assessed weekly for IBS symptoms over the active treatment phase. We used a complier average causal effect (CACE) analysis, in the growth mixture modeling framework, to (1) examine the specific effect of exposure among those who received the intervention (i.e. compliers), and (2) explore the associations of pre-treatment patient characteristics with compliance status and outcome changes.

Results

Fifty-five per cent of those assigned to the experimental condition were classified as compliers. The CACE analysis that took into account compliance status demonstrated that the magnitude of the incremental effect of systematic exposure on IBS symptoms was larger than the effect observed in an intention-to-treat analysis that ignored compliance status (d = 0.81 v. d = 0.44). Patients with university education showed more improvement during the exposure phase of the treatment. Pre-treatment patient characteristics did not predict compliance status.

Conclusions

The effect of systematic exposure on IBS symptoms is of substantial magnitude among those individuals who actually receive the intervention (CACE). Studying the subsample of individuals who discontinue treatment prematurely and tailoring interventions to improve compliance may increase overall improvement rates in ICBT for IBS.

Type
Original Articles
Copyright
Copyright © Cambridge University Press 2017 

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