Evaluating the Effectiveness of an Online Small-Group Self-Management Workshop for Rural Caregivers of Individuals With Alzheimer's Disease and Related Dementias
Phase: NA
Conditions: Depression, Stress, Psychological, Self Efficacy, Loneliness, Social Isolation, Health Care Utilization, Dementia, Dementia Alzheimers, Dementia of Alzheimer Type, Dementia, Vascular, Dementia Frontal, Dementia, Lewy Body, Dementia, Mixed, Dementia in Parkinsons Disease, Dementia, HIV, Dementia Frontotemporal, Dementia, Multi-Infarct
Sponsor: University of California, San Francisco

Statistical Power Considerations in Building Better Caregiver Study 
Study: R01 AG057855-01 
PI: Veronica Yank 
Date: 11 August 2019 
NCT04428112 
This document is a response to the DSMB recommendation: “The study team should provide a written 
explanation and revision to account for the changes in power calculations, particularly regarding drop-
out rates.” 
Summary from study team. The statistical power consideration was revised based upon updated information 
on the challenges in the recruitment and retention provided by the study team. The study team, which includes 
the study biostatistician, has selected the randomization approach “Varying (flexible) randomization ratio (1:1, 
2:1, 3:1)” described below based on changes in expected retention and power calculations also described 
below. 
The original statistical power consideration was based on 1:1 randomization to treatment and control. 
Assuming 70% retention rate, 448 caregivers at the end of the study will allow us to detect an effect size of 
0.265 in the primary outcome PHQ-8 depression symptoms score with a power of 0.80 at a significance level 
of 0.05 (two-sided). The effect size of 0.265 corresponds to about 1.5 difference in PHQ-8 score (range 0-24) 
between groups assuming a common standard deviation of 5.6 (Lorig K, Thompson-Gallagher D, Traylor L, et 
al. Building Better Caregivers: a pilot online support workshop for family caregivers of cognitively impaired 
adults. Journal of Applied Gerontology. 2012;31:423-437.)  
The recruitment and retention challenge came to light based on new information from the accumulated 
experience with the VA BBC workshop, which has enrolled over 5,000 Veteran caregivers. Unpublished data 
made available to the study team demonstrates that if caregivers’ respective assigned workshops do not start 
within 2 weeks, they quickly lose interest and do not attend the workshops. This new data prompted the current 
study team to reconsider the recruitment, randomization, and retention plan. The study team recognized that if 
study enrollment could not accrue fast enough to fill both a workshop group and attention control group within a 
2-week period (i.e., total of 54 participants per 2-week period) at 1:1 randomization, then retention would drop
precipitously similar to what has been documented for some VA caregivers. The new data suggest that the
original 1:1 randomization plan may lead to a retention rate of 50%, and 320 caregivers at the end of study will
provide a power of 0.66 to detect the same effect size of 0.265.
The revised statistical power consideration was based on randomization with ratios of 1:1, 2:1 or 3:1 to 
treatment and control, depending on the actual recruitment process of participants within each 2-week period 
of recruitment. The 2:1 and 3:1 randomizations are expected to help with the recruitment and retention.  
Fixed randomization ratio (2:1, 3:1) 
Assuming that a fixed ratio of 2:1 will be used in randomization and the retention rate will increase from 50% to 
75%, then the sample size of 480 caregivers (320 in treatment and 160 in control) at the end of the study will 
provide us a power of 0.78 to detect the same effect size of 0.265. 
Assuming that a fixed ratio of 3:1 will be used in randomization and the retention rate will increase from 50% to 
75%, then the sample size of 480 caregivers (360 in treatment and 120 in control) at the end of the study will 
provide us a power of 0.71 to detect the same effect size of 0.265. 
Varying (flexible) randomization ratio (1:1, 2:1, 3:1) 
If enough caregivers are enrolled in a 2-week period (e.g., 54) to use a 1:1 randomization, that will be used; if 
there are somewhat fewer (e.g., 41), 2:1 randomization will be used; if fewer (e.g., 36), 3:1 randomization will 
be used. Use of this flexible approach has achieved high retention rates in the prior trials (e.g., Lorig KR, Sobel 
DS, Stewart AL, et al. Evidence suggesting that a chronic disease self-management program can improve 
health status while reducing hospitalization: a randomized trial. Medical care 1999;37:5-14). Assuming that the 

randomization with varied ratios will increase the retention rate from 50% to 75% and the randomization ratio 
will be controlled for as a categorical variable in the analysis model, 480 caregivers at the end of the study will 
allow us to detect a partial correlation of 0.13 between the treatment and outcome with a power of 0.82 at a 
significance level of 0.05 (two-sided).   
 
Randomization 
plan 
Total 
sample size 
Retention 
rate 
# participants at 
the end of the 
study 
Power 
Effect size 
Original 1:1 
640 
70% 
448 
0.80 
0.265  
(a treatment group difference of 
1.5 in PHQ-8 score) 
Original 1:1 but 
with revised 
downward 
estimate of 
retention based on 
new information 
from VA 
640 
50% 
320 
0.63 
0.265 
Fixed 2:1 
640 
75% 
480 
0.78 
0.265 
Fixed 3:1 
640 
75% 
480 
0.71 
0.265 
Varying 1:1, 2:1, 
3:1 
640 
75% 
480 
0.82 
A partial correlation of 0.13 
between treatment and PHQ-8 
score.