How Long Should a Behavioral Activation Single-session Intervention be? A Four-armed Trial Comparing Effectiveness by Intervention Duration
Phase: NA
Conditions: Depression
Sponsor: Northwestern University

 
 
 
 
 
 
 
 
 
 
 
Study Protocol and Statistical Analysis Plan 
How Long Should a Behavioral Activation Single-session Intervention be? A Four-armed 
Trial Comparing Effectiveness by Intervention Duration 
ClinicalTrials.gov ID NCT06313736 
April 17, 2024 
 
 
 
 
 
 
 
 
 
 
 
 
 

Protocol 
Researchers will use the crowdwork platform CloudResearch Connect to recruit and 
compensate participants. Researchers will pay participants $0.25 USD for completing 
the screener and (if eligible) the study information sheet. If participants are eligible, 
researchers will send them invites through the crowdwork platform to participate in the 
next parts of the study. Researchers will pay them $4.00 for completing session 1 of the 
study and $1.00 for the 8-week follow-up. Participants are only allowed to complete the 
study once and cannot participate in the study if they have participated in another study 
from the research team relating to depression on CloudResearch Connect in the last 
two months. 
 
Researchers will recruit a sample of 1,100 adults who struggle with depression. To 
recruit these adults, potential participants will complete a screener and, if eligible, read 
the study content information and decide whether to participate (2 minutes). Within five 
days, participants who consent will be invited to complete the first part of the study. In 
this part, they will first complete a questionnaire of demographics and well-being at 
baseline (roughly 4 minutes), be randomly allocated to one of four conditions with equal 
odds of assignment to each condition, complete the SSI to which they were randomized 
(2-15 minutes) and then complete the post-test measures (roughly 4 minutes) just after 
the SSI and eight weeks later. Combined across all three study sessions, the study 
should take roughly 29 minutes. At the end of the study, researchers will offer 
participants access to a list of free online mental health support resources (shown in 
supporting documents). At the end of the study, researchers will also offer participants 
permanent access to all four SSIs. 
 
The research team created the SSIs of different lengths aiming to make the active 
elements in each SSI as consistent as possible. Thus, even though the 2-minute 
version contains less content than the 15-minute version, researchers tried to ensure it 
expresses the same general message and activates similar mechanisms of change. 
Participants will complete questionnaires asking about their well-being and experiences 
with the interventions at baseline, post-test, and 8-week follow-up. 
 
All interventions and survey materials are available at https://osf.io/g846j. 
 
Statistical Analysis Plan  
Main analysis: The main DV is change in depressive symptoms (PHQ-8) from baseline 
to 8-week follow-up. The main analysis compares change in PHQ-8 score from baseline 
to 8-week follow-up across experimental conditions. Researchers will use a mixed-
effects model predicting depressive symptoms with condition, measurement time point 
(1 = baseline, 2= 8-week follow-up), and the 2-way interaction between condition and 
measurement time point as IVs and a participant identifier as a random intercept. Using 
the “lme4” package in R, these analyses will take the following form: 
 

lmer(phq8 ~ time*condition + (1|pid)) 
 
Secondary analysis: Researchers will re-run the same analysis as above separately for 
each secondary outcome collected. Researchers will also duplicate the main analysis 
but with the following covariates included in the mixed-effects model: gender (multiple 
choice), age (continuous), ethnicity (categorical), education level (categorical), 
employment (categorical), and if one completed the study on a phone (binary). 
 
Inference criteria 
For all analyses, researchers will use the standard p < 0.05 criterion for determining 
statistical significance. Researchers will use two-tailed tests for each of researchers’ 
analyses. 
 
Data exclusion 
Main analyses will be limited to only those participants who 1) were randomized to a 
condition (i.e., those who consented to participate and completed the baseline 
measures), 2) did not indicate that they did not participate seriously at the end of the 
study, and 3) completed the study only once. 
 
Missing data 
Based on researchers’ previous work on Cloudresearch Connect, researchers do not 
foresee a great deal of missing data or differential dropout. Although researchers will 
take efforts to avoid missing data (e.g., a financial incentive for completing the study 
and reminder emails), it is not necessary to impute missing data before performing a 
longitudinal mixed-model analysis (Twisk et al., 2013). Participants with missing data at 
some assessments will be included in the analysis and results will be modeled on the 
basis of the available data.