Online Trial Examining Validity and Reliability of the Shared Decision Making Process Survey in Adults With Depression
Conditions: Depression
Sponsor: Massachusetts General Hospital

Study Title: Examining Validity and Reliability of the Shared Decision Making Process Survey in 
Adults With Depression 
 
Document Title: Design and Analysis plan for a study examining validity and reliability of the 
shared decision making process survey in adults with depression 
 
PI: Karen Sepucha, PhD (ksepucha@mgh.harvard.edu) 
 
Statistician: KD Valentine, PhD 
 
ClinicalTrails.gov: NCT04343534 
 
Date: March 15, 2023 
 
 

Purpose: 
The purpose of this study is to test two differently worded versions of the Shared Decision Making 
Process scale in a sample of adults who have recently made a decision about treatment of 
depression. The main goals are to gather evidence of reliability, to test whether the generic version 
has similar psychometric performance to the original, and to extend generalizability of the findings 
to younger adults. 
 
Design: 
Staff worked with a national sampling firm to recruit subjects and obtain 500 responses to the 
baseline survey (n=250 for each version) and a subset will complete a retest survey (n=200; 50 from 
each age and survey type group). Eligible subjects are adults aged 18-75 who talked with a health 
care provider about treatment for depression in the preceding 12 months. The sample is not a 
national probability sample; however, the recruitment efforts will ensure about 50% of respondents 
aged 18-39 and 50% aged 40-75, and to ensure at least 25% of the sample is racial/ethnic minorities 
(Black or African American, Asian, Hispanic or Latino). 
Subjects are randomly assigned to one of the two versions of the Shared Decision Making Process 
scale and complete a set of measures regarding their experiences with decision making for 
depression, demographics, and health status. A subset of respondents will complete the Shared 
Decision Making Process scale again 1 week later to examine short term test-retest reliability. 
 
Randomization and Blinding: 
Participants in each study were randomly assigned by the sampling firm to complete one of the two 
versions of the Shared Decision Making Process scale. Participants were blinded to their version, but 
no other blinding occurred.  
 
Primary Outcome: 
• SDM Process scale [baseline and retest]. The SDM Process scale measures the amount of 
SDM that occurs in an interaction. For this project, the scale items were adapted to be 
completed by an observer rather than a participant in the interaction. Scores range from 0 to 
4; larger values indicate greater SDM occurred. This scale was altered so that one group 
received the original version with risks and benefits discussed as reasons not to [insert 
treatment], and reasons to [insert treatment], while the other completed the alternative 
version where risks and benefits were discussed as downsides of [insert treatment] and 
benefits of [insert treatment].  
Secondary Outcome: 
• Decisional conflict: The SURE scale is a 4-item short form of the decisional conflict scale. 
The response options are true or false and scores range from 0-4. Scores of 4 are considered 
top scores (no decisional conflict) while all scores less than 4 are indicative of some 
decisional conflict.  
• Decisional regret: A single-item asked respondents if they would make the same decision 
now about how to treat their depression. Response options were 1=definitely yes, 2=probably 
yes, 3=probably no and 4=definitely no. Higher scores indicate more regret.  
• Who made the decision: a single item asked respondents who made the final decision about 
how to manage their depression. Response options included ‘mainly my decision’, ‘’mainly 
the healthcare providers decision’, and ‘we made the decision together’. We compared those 
who made the decision alone or with the healthcare provider to those he said the healthcare 
provider mainly decided. 

 
Sample Size:  
The sample size was determined to ensure sufficient power to detect differences in key subgroups, 
including age (younger adults vs. older adults) and version (A vs. B). To detect a difference of about 
0.33 standard deviations at 0.05 significance with 80% power would require 125 per group.. 
 
Statistical Methods: 
Demographic data were examined using descriptive statistics by younger and older age groups, as 
well as by version groups. Differences between the groups were examined using two sample t-tests 
for continuous variables and chi-square analyses for categorical variables. 
 
The SDM Process scale and items were compared by age group and version to determine if the 
scores spanned the range of total possible scores, were normally distributed, had low rates of 
missing data and whether there was evidence of floor or ceiling effects. 
 
Data were analyzed to compare the version (A versus B) and age group (younger versus older) by 
participant characteristics, SDM Process scale items and construct validity to determine if there were 
differences. If differences did not exist, we planned to combine the data for the analyses. As there is 
no gold standard measure of SDM, we used the following hypotheses to test the construct validity of 
the scale given prior work. 
1) Respondents with higher SDM Process scores would be more likely to report no decisional 
conflict. To test this, we used we used two 2 (group) × 2 (no conflict v. some conflict) analyses of 
variance—one that looked for differences in the relationships between decisional conflict and SDM 
Process score by age group and one by version. 
2) Respondents with higher SDM Process scores would have less regret. We used independent 
correlations to test if the relationship between SDM Process scores and regret scores differed by age 
group or version group. 
3) Respondents who report that their decision-making process was mainly driven by the health-care 
provider will have lower SDM Process scores than those who report that they were more involved in 
selecting the treatment. To test this, we used we used two 2 (group) × 2 (mainly healthcare provider 
v. patient involved) analyses of variance—one that looked for differences in the relationships 
between decision making process and SDM Process score by age group and one by version. 
 
We assessed the retest reliability for the SDM Process score at retest and compared by version (A 
and B) and by age group (younger and older) using the intraclass correlation coefficient (ICC>.7 
indicating reliability).