Enhancing the Acceptability of Psychological Treatments for Obsessive-compulsive Disorder
Phase: NA
Conditions: Obsessive-Compulsive Disorder
Sponsor: Concordia University, Montreal

 
 
Enhancing the Acceptability of Psychological Treatments for 
Obsessive-Compulsive Disorder 
 
 
 
 
Study Protocol and Statistical Analysis Plan 
 
 
 
 
 
 
 
 
 
 
 
Unique Protocol ID: 30006258 
Date: July 20, 2018 
  
 
 

Study Protocol 
 
Individuals who contact the clinic expressing interest in the study will first complete a telephone screen 
in order to assess their potential eligibility. Screener questions from the ADIS-V will be used to 
determine their likely inclusion in the study; those who seem likely to be eligible will be invited to the 
clinic to complete a baseline assessment, consisting of the ADIS-V and YBOCS, as well as measures of 
OCD, anxious and depressive symptomatology and demographic and treatment history measures.  
We will administer several measures to assess treatment acceptability. These will include the 
Credibility/Expectancy Questionnaire (CEQ), and the Treatment Acceptability / Adherence Scale (TAAS). 
The CEQ and TAAS will serve as subjective measures; objective measures will include counts of 
treatment refusers and dropouts across the two treatments. A refuser is defined as a participant who is 
deemed eligible following the initial assessment, but who declines to continue at any time after 
randomization, but before session 2 (the first session is for case formulation, treatment planning, and 
includes a comprehensive description of the treatment approach). A dropout is defined as a participant 
who withdraws their participation from the study any time after the beginning of session 2. Should any 
participant refuse or drop out of CT or ERP, we will ask them to list their reasons for this decision. 
In addition to the Anxiety Disorders Interview Schedule (ADIS-V), we will administer the Yale-Brown 
Obsessive-Compulsive Checklist (YBOCS). Diagnostic and interview reliability will be assessed via a 
second trained rater who will listen to and rate recordings of interviews. In instances where there is 
disagreement on diagnostic status, a team meeting will be held to discuss the issues and resolve the 
discrepancy. Self-report measures assessing OCD symptoms (i.e., Vancouver Obsessional Compulsive 
Inventory, VOCI), OCD beliefs (Obsessional Beliefs Questionnaire, OBQ), process measures (e.g., 
Personal Significance Scale, PSS), as well as measures of depression and anxiety symptomatology (Beck 
Depression Inventory, 2nd Ed, BDI & Beck Anxiety Inventory, BAI) will be administered. 
Eligible participants will be block randomized (to ensure equal numbers of participants per treatment 
condition) via www.randomizer.org, and will begin session 1 of either ERP or CT with one of 2 therapists 
(see below). Participants will be asked to complete the PSS and VOCI before the start of each session. At 
all time points, assessors will be blind to treatment assignment, such that they will not know whether a 
participant has been offered or is receiving ERP or CT. After the 3rd, 6th, and 12th and final session, and 
at each follow- up point, participants will be asked to complete the CEQ and TAAS in order to assess 
their views of the acceptability of the treatment they receive. After session 6, participants will complete 
a mid-therapy assessment consisting of the YBOCS, VOCI, OBQ, PSS, BAI and BDI.  
This RCT will involve trial administration (shared by the Investigators and the study coordinator), an 
assessment team (research assistant and graduate student), and a team of 3 therapists (post-doctoral 
fellow(s) and a senior graduate student). This will allow for comparisons of therapist effects, as well as 
the effects of therapist experience on outcome and acceptability. The first 6 months of the project are 
reserved for training team members on relevant tasks. Training will be overseen by the NPA, and offered 
by all project investigators.  

ERP (12 sessions) will be based on a standard, commonly-used manual, and will comprise 1 session of 
case formulation and treatment planning, 10 sessions of ERP, plus 1 final session on relapse prevention. 
Exposures in this protocol are prolonged and repeated, requiring clients/patients to engage in a series of 
exposures to feared stimuli (e.g., contaminants, doubts, intrusive thoughts), and to refrain from 
engaging in compulsive behaviour until their anxiety subsides. ERP is well-established, and known to be 
highly effective for OCD.  
CT (12 sessions) will be modularized, and based on elements from our three primary treatment 
packages. It will begin with 1 session of case formulation and treatment planning, followed by 10 
sessions focused on evidence gathering and behavioural experiments (which are importantly different 
from prolonged exposure), plus 1 final session on relapse prevention. The 3 treatment packages share a 
number of common features – they include focus on reducing inflated responsibility, target the personal 
significance of the participant’s thoughts or compulsions, etc. Each also incorporates other elements 
specific to the primary symptom (e.g., beliefs about memory in compulsive checking, a perceived 
violation in mental contamination, or thought-action fusion in association with obsessions), allowing CT 
to be tailored to the individual beliefs and concerns of each participant. Many of these cognitive areas of 
focus are highly novel, and have not been assessed in previously conducted RCT’s of CT, although our 
focus on problematic beliefs and appraisals in general is entirely consistent with established CT for OCD 
packages.  
All sessions will be recorded in situ for the purposes of assessing treatment fidelity; this will be done on 
an ongoing basis via trained coders, blind to hypotheses and to condition assignment who will be asked 
to assess the proportion of session content allocated to a focus on behaviour/exposure vs. 
cognition/reappraisal. Audio recording devices will be made available to participants and their use is a 
standard enhancement of treatment interventions to help make them more memorable, and to clarify 
any questions that may arise between sessions.  
At the end of treatment, and at 6- and12-month follow-up periods, participants will complete the mid-
therapy assessment measures again, in addition to the ADIS-V. 
 
 

Statistical Plan 
 
Primary hypotheses will be tested by comparing our indices of acceptability across the two treatments. 
Specifically, participant ratings of treatment acceptability, and the relative numbers of treatment 
refusers and dropouts will be assessed. Independent samples t-tests will be used to compare the two 
treatments groups on self-reported treatment acceptability on the CEQ and the TAAS. Furthermore, chi-
squared tests will be used to compare treatments on the number of refusers and drop outs. 
Completer and intent-to-treat analyses will be conducted on YBOCS and VOCI total scores (i.e., OCD 
symptom severity) measured at multiple time points. ANCOVA will compare treatments on changes in 
OCD symptom severity across all measurement periods, with baseline scores as covariates. Although we 
have reason to suspect that our CT may outperform more traditional cognitive approaches to the 
treatment of OCD, we expect that both ERP and CT will be similarly effective (as has been shown in 
numerous trials, and in a recent comprehensive review), perhaps with intent-to-treat analyses showing 
a small advantage of CT over ERP, yet we do not expect to be powered to detect significant differences.