Evaluating a Web-based Intervention for Reactions to Suicidal Thoughts
Phase: NA
Conditions: Suicidal Ideation
Sponsor: Florida State University

Study Protocol and Statistical Analysis Plan 
 
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Evaluation of a Computerized Intervention for Learning to Re-Evaluate Suicidal Thoughts 
 
NCT04254809 
 
[Date: 4/27/2021] 
 
 
 
 

Study Protocol and Statistical Analysis Plan 
 
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Background. 
As rates of suicide have increased over the last several decades, research has identified 
that roughly two-thirds of individuals who attempt suicide do so within one year from the time 
that they begin to think about suicide. This suggests a greater need for interventions designed 
to specifically help individuals learn to cope with thoughts of suicide to interrupt the process by 
which thoughts may lead to suicidal behaviors (i.e., attempts). It is common that individuals with 
suicidal ideation may not understand where thoughts of suicide come from and are therefore 
distressed at the prospect they might never escape these thoughts. As a result, these 
individuals may attempt to distract from or avoid these thoughts in ways that contribute to 
suicidal ideation becoming more frequent and intense over the long-term. This 'experiential 
avoidance' of suicidal ideation is therefore an excellent target for treatment and has in fact been 
shown to help reduce the distress associated with suicidal thoughts in several treatment studies. 
The intervention to be tested in this study seeks to reduce the distress related to suicidal 
thoughts by explaining that these thoughts are a normative response to extreme stress, and 
provides strategies that help individuals observe that suicidal thoughts are temporary (i.e., will 
not last "forever") and something they can tolerate without needing to rigidly control them. To 
maximize the potential of this intervention to help the largest number of individuals, it is entirely 
computerized and takes only 30 minutes to complete. This will help reduce many of the 
traditional barriers to treatment that individuals with suicidal ideation face (e.g., costs, time 
restrictions, and stigma of help-seeking). 
Objectives. 
Individuals (N=106) with current suicidal ideation will be randomly assigned to participate in 
either the experiential avoidance intervention for suicidal thoughts or a control intervention. 
Experiential avoidance (i.e., distress or avoidance) and severity of suicide risk will be measured 
one week, and one month after participants complete their assigned intervention. It is 
hypothesized that, compared to controls, individuals who receive the experiential avoidance 
intervention will report: 1) less experiential avoidance at one week follow-up, and 2) less severe 
suicide risk at one-month follow-up. 
Design. 
This is a double-blinded randomized treatment trial with two-arms (active and control 
conditions). 
Power Analysis. 
An a prior power analysis was conducted. Expected effect size was estimated given the 
reported effect of a similar single-session computerized intervention in a prior study. Compared 
to a health intervention control, Schmidt, Norr, Allan, Raines, and Capron  (2017) reported a 
small-sized effect (f = .18) of a brief computerized intervention for Anxiety Sensitivity on pre-
intervention to one-month change in BSS suicidal ideation scores among participants (N = 72) 
with current suicidal ideation. Like REST, the active intervention described in that study was 
delivered by computer, sought to de-catastrophize cognitive symptoms of mental dyscontrol and 
anxiety, and led participants through exercises to demonstrate a sense of control over mental 
and physical symptoms of anxiety. Projecting a similar small-sized (f = .18) main effect of REST 
on BSS suicidal ideation at one-month follow-up, estimating power to be 80%, and using an 
alpha value of .05, a two-group a priori repeated measures (i.e., pre-intervention and one-month 
follow-up) power analysis conducted in G*Power (version 3.1.9.2) suggested a sample size of 
88. To further account for a 20% attrition rate at one-month follow-up, 106 participants were 
anticipated to be recruited for this study. 

Study Protocol and Statistical Analysis Plan 
 
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Methods. 
At the baseline appointment participants provided written informed consent to participate 
in the study. Next, they completed a battery of self-report measures including the AAQ-SI, 
WBSI-SI, and BSS. Next, participants completed their assigned intervention condition from a 
desktop computer in a private room. Participants were assigned to intervention condition 
according to a random numbers table that was created prior to participant recruitment. Following 
the intervention all participants completed the AAQ-SI. Participants then spent two minutes 
writing about their recent suicidal thoughts, followed by a five-minute thought monitoring period, 
after which they completed the WBSI-SI to measure avoidance of suicidal ideation during the 
thought monitoring period. Lastly, a graduate-level clinician collaborated with participants to 
generate a safety plan for mitigating risk of future suicide attempt. Participants were then 
debriefed on the day’s appointment, scheduled for their one-week follow-up check-in, and 
compensated ($20 or two research credits) for participation.  
At the one-week follow-up appointment participants were sent an email containing a 
web-link to complete a battery of self-report follow-up questionnaires including the AAQ-SI, 
WBSI-SI, and BSS via Qualtrics. Completion of this survey triggered an email alert to study 
personnel, after which a suicide risk check-in was conducted over the telephone with a 
graduate-level clinician. Clinicians also helped participants update their individual safety plans 
as needed. Participants were then reminded of the date for their one-month follow-up check, 
and confirmed compensation for that appointment ($5 Amazon gift card or 0.5 research credits. 
These same procedures were followed for the one-month follow-up appointment, with the 
addition of debriefing following the one-month appointment. All participants in the control 
condition were offered the opportunity to complete the REST intervention following their last 
follow-up appointment. All procedures were approved by the Florida State University 
Institutional Review Board. 
Statistical Analysis Plan. 
Power Analysis. An a prior power analysis was conducted. Expected effect size was 
estimated given the reported effect of a similar single-session computerized intervention in a 
prior study. Compared to a health intervention control, Schmidt, Norr, Allan, Raines, and Capron  
(2017) reported a small-sized effect (f = .18) of a brief computerized intervention for Anxiety 
Sensitivity on pre-intervention to one-month change in BSS suicidal ideation scores among 
participants (N = 72) with current suicidal ideation. Like REST, the active intervention described 
in that study was delivered by computer, sought to de-catastrophize cognitive symptoms of 
mental dyscontrol and anxiety, and led participants through exercises to demonstrate a sense of 
control over mental and physical symptoms of anxiety. Projecting a similar small-sized (f = .18) 
main effect of REST on BSS suicidal ideation at one-month follow-up, estimating power to be 
80%, and using an alpha value of .05, a two-group a priori repeated measures (i.e., pre-
intervention and one-month follow-up) power analysis conducted in G*Power (version 3.1.9.2) 
suggested a sample size of 88. To further account for a 20% attrition rate at one-month follow-
up, 106 participants were anticipated to be recruited for this study. 
Equivalence of Random assignment. Equivalence of random assignment to condition 
was evaluated with independent sample t-tests for continuous variables and chi-square tests of 
independence for categorical variables. There were no significant differences observed between 
intervention conditions for any demographic variables (e.g., age, sex, race; all p’s > .622) or 
psychological variables at baseline (e.g., AAQ-SI, WBSI-SI, BSS; all p’s > .210) 
Missing Data. All variables were evaluated for missing data at each study time point. No 
missing values were identified at the baseline, post-intervention, or thought monitoring time-
points. At one-week follow-up there were four values (4.2% of cases) missing. At one-month 

Study Protocol and Statistical Analysis Plan 
 
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follow-up there were 20 values missing (20.8% of cases). Little’s test for data MCAR was non-
significant (2[38] = 48.42, p = .120), suggesting that values were indeed MCAR. The a priori 
plan for handling longitudinal missing data, assuming data MCAR and equivalence of random 
assignment, was to replace missing values with the last-observation-carried-forward method. 
Differences among completer samples.  Baseline differences were evaluated among 
individuals who complete the one-month follow-up (i.e., completers) and those who were lost-to-
follow-up (i.e., non-completers). Equivalence of random assignment to condition was evaluated 
with independent sample t-tests for continuous variables and chi-square tests of independence 
for categorical variables. There were no differences among those who provided complete data 
versus those who were lost to follow-up on any demographic variables (all p > .511) or baseline 
psychological variables (all p’s > .249). Similarly, there were no significant differences between 
conditions with respect to completer status, 2(1) = 1.64, p = .200. 
Assumptions of Normality. All self-report outcome variables were assessed for 
skewness, kurtosis, and outliers. Outliers were hand-corrected utilizing the interquartile range 
(IQR), to fall at the value 1.5xIQR +/- Q3/Q1. No AAQ-SI data were corrected. Five low-lying 
outliers were corrected to Q1-1.5xIQR for the WBSI-SI. One high value was corrected to 
Q3+1.5xIQR for the BSS. After correction, all values evidenced acceptable skew and kurtosis 
values of < |2|.  
Change scores. Standardized residualized change scores were calculated for all 
outcome variables by regressing scores of each measure at the follow-up time point (i.e., one-
week for AAQ-SI and WBSI-SI, and one-month for BSS) onto scores of their respective baseline 
measure.  
Primary Analyses. All analyses were conducted in SPSS Version 26. To examine the 
first primary outcome, the direct effect of condition on change in distress of suicidal ideation at 
one-week, a linear regression model was conducted with condition as the independent variable 
and standardized residualized change in AAQ-SI the dependent variable. To examine the 
second primary outcome, the direct effect of condition on change in suicidal ideation severity 
one-month, a linear regression model was conducted with condition as the independent variable 
and standardized residualized change in BSS the dependent variable. 
Secondary Analyses. To examine the first secondary outcome, the direct effect of 
condition on change in avoidance of suicidal ideation at one-week, a linear regression model 
was conducted with condition as the independent variable and standardized residualized 
change in WBSI-SI the dependent variable.