Skip to main content

Table 4 Trial conduct solutions to treatment contamination

From: A scoping review of the problems and solutions associated with contamination in trials of complex interventions in mental health

Process driving contamination Trial conduct solution Number of papers
Clinicians deliver both active and control treatments Recruiting groups of clinicians, each one of which is responsible for a single treatment 16
Monitoring contamination using supervision/therapy session recordings 10
Formalising differences between interventions, e.g. using structured manual during therapist training 6
Asking clinicians not to use intervention content when treating those in control arm 3
Providing active intervention within the research project rather than health service 1
Using a script for contact with control participants during treatment 1
Clinicians not involved in active intervention treating participants in both trial arms Blinding usual care clinicians 4
Confining intervention to provision by specialist clinicians 2
Communication between clinicians in different trial arms Asking clinicians not to share details of the intervention with each other 5
Communication between participants in different trial arms Holding treatment sessions at different times / in different locations 13
Staggering the scheduling of data collection appointments / reducing waiting time so that participants do not meet in waiting room 3
Allocating separate therapists / modes of delivery for individual and group therapies when usual group therapy was shared by participants in both arms 2
Asking participants not to share contents of intervention with others 2
Excluding potential participants who know someone else attending screening 2
Holding separate sessions of existing group treatments for participants in separate trial arms in order to prevent contact 1
Restricting the release of intervention materials in order to reduce the chance of their being shared with control participants 1
Recruiting participants in blocks and providing one treatment at a time, with no new participants recruited during the final week of each period in order to maintain separation between trial arms 1
Participants switching clinicians and therefore trial arms Preventing referrals for add-on care by clinicians who are members of study team 1
Avoiding transfer of participants between clinicians 1
Participants seeking treatment outside the trial Informing participants only about the treatment they were allocated to receive (Zelen’s design) 8
Promising the intervention to control participants at the end of follow-up 2
Active treatment is available to some extent within the healthcare system Making intervention distinct from usual care by adapting one or other 2
Establishing common treatment for all participants 1
Excluding institutions that already offer some aspect of the intervention 1