Predictors of study retention in addiction treatment trials
KORTE JE1, MAGRUDER KM1,2, KILLEEN TK1, SONNE SC1, SAMPSON RR1 and BRADY KT1,2
1. Medical University of South Carolina, Charleston, South Carolina, USA
2. Ralph H. Johnson VA Medical Center, Charleston, South Carolina, USA
Predictors of study retention in addiction treatment trials
KORTE JE1, MAGRUDER KM1,2, KILLEEN TK1, SONNE SC1, SAMPSON RR1 and BRADY KT1,2
1. Medical University of South Carolina, Charleston, South Carolina, USA
2. Ralph H. Johnson VA Medical Center, Charleston, South Carolina, USA
Design
•Secondary data analysis
•Pooled analysis of randomized controlled trials for drug addiction treatment
•First fifteen protocols in NIDA Clinical Trials Network (CTN) with datasets locked andappropriate for analyses of client retention during follow-up
•CTN 01, 02, 03, 04, 05, 06, 07, 09, 10, 11, 13, 15, 18, 19, 21
Retention definition
•Study-specific definition of retention
•Based on whether each client completed the final study assessment at which themajor outcome variable was collected (as defined by the respective study protocols)
Study Population
•Each protocol included individuals meeting specific criteria for drug use (criteria variedby protocol)
•Participants were included in the retention analyses if they met study criteria and wererandomized.
Follow-up
•Scheduled study visits varied by protocol (see Table 1)
Analysis
•Preliminary analyses: chi square for bivariate associations
•Logistic regression modeling to predict the odds of retention during follow-up
•Main predictors of interest: gender and ethnicity
•Stratified model by whether clients had taken prescribed methadone in 30 daysbefore study baseline
•Other covariates: age, length of study follow-up
NIDA Blending Conference, Albuquerque NM • April 22-23, 2010
RESULTS
INTRODUCTION
OBJECTIVE
METHODS
SUMMARY AND CONCLUSIONS
Clients on methadone were seen to have better retention than other clients;further, among clients on methadone, other potential predictors were notstrongly related to retention in study follow-up.
Among clients not on methadone, Caucasians were most likely to be lost tofollow-up, and Hispanic/other clients were least likely. Women were 15%less likely to be lost to follow-up in comparison to men. In particular,Hispanic/other women had better retention than any other group.
By improving our ability to identify clients at increased risk of loss to follow-upduring research studies, we can devise strategies to maximize retention forall participants. Future analyses will take into consideration other client andprotocol characteristics to further refine our assessment of factors related toretention during follow-up.
Differential attrition in research studies is a threat to study validity. Attrition during thetreatment phase of a study should be conceptualized and studied separately fromattrition during follow-up. Unbiased assessment of intervention effectiveness requiresgood follow-up rates, and roughly equivalent follow-up rates between groups. Byfocusing on retention during follow-up, we can improve our ability to maximize internaland external validity of study results.
The current study is focused on attrition during follow-up, which is primarily relevant forvalid ascertainment of research outcomes (as opposed to retention during treatment,which is relevant for both research outcomes and treatment planning).
We examined predictors of follow-up completion in the first 15 protocols to have lockeddatasets in the NIDA Clinical Trials Network (CTN). We focused on gender and ethnicityas the main predictors of interest.
The objective of the current study is to improve our understanding of why certain types ofclients are lost to follow-up, in order to design better study procedures to maximizeretention for all participants.
In preliminary analyses, we observed large differences in retention between different CTN protocols (Table 2).
Some of these differences are attributable to structural protocol characteristics (e.g. length of follow-up), or attributable to differences in the proportion of clients inmethadone maintenance programs (expected to increase retention).
In multivariate models of retention, we found that use of prescribed methadone during the last 30 days, as expected, was a highly significant predictor of retentionduring follow-up, with clients on methadone less than half as likely to be lost to follow-up (p<0.001).
Stratifying by methadone status in logistic regression models (Table 4), we found that among methadone clients, no retention differences were seen by age, race,gender, or length of study follow-up. In contrast, among clients not using prescribed methadone, we found highly significant differences. In comparison to AfricanAmericans, white clients were 50% more likely to be lost to follow-up, whereas Hispanic/other clients were 30% less likely. Longer length of study follow-up wasassociated with better retention; this finding bears further investigation and may be due to other study/client characteristics. Finally, in both methadone and non-methadone clients, we found that women were 15% less likely to be lost to follow-up; this finding was significant in overall models and among non-methadone clients,but not among models limited to methadone clients.
We observed a significant interaction between ethnicity and gender in relation to study retention: this interaction was largely driven by Hispanic/other women not inmethadone treatment, who were approximately 40% less likely to be lost to follow-up than their African American counterparts. In contrast, white women (not inmethadone treatment) were approximately 20% more likely to be lost to follow-up than their African American counterparts.
1
2
3
4
5
6
7
9
10
11
13
15
18
19
21
Race/ethnicity
Caucasian
59%
41%
71%
42%
84%
38%
28%
36%
70%
64%
37%
49%
48%
58%
0%
African American
21%
38%
11%
42%
12%
45%
54%
24%
0%
35%
33%
35%
25%
24%
0%
Hispanic
20%
22%
18%
16%
4%
16%
18%
40%
30%
1%
30%
17%
27%
18%
100%
Gender
Female
59%
28%
33%
71%
58%
55%
43%
48%
42%
37%
100%
100%
0%
100%
11%
Age (mean)
36.0
38.3
35.9
35.3
33.1
35.2
41.5
42.1
19.7
36.2
26.2
39.2
39.5
38.8
32.7
Retained to final follow-up visit
83%
80%
51%
68%
75%
68%
83%
80%
60%
72%
74%
77%
68%
65%
78%
Using prescribedmethadone in last 30days
1%
1%
1%
4%
0.4%
1%
100%
72%
3%
3%
12%
13%
51%
59%
2%
CTNprotocolnumber
Type ofintervention
Visit schedule
Retentiondefinition
1
Medication trialfor inpatientopiate detox
13 days detox;then follow-up at1, 3, and 6months
13-day end oftreatment
2
Medication trialfor outpatientopiate detox
13 days detox;then follow-up at1, 3, and 6months
13-day end oftreatment
3
Suboxone taper:comparison oftwo schedules
4 weeks ofstabilization;then 7 or 28days of taper;then follow-up at1 and 3 monthspost-taper
3-month follow-up
4
Motivationalenhancement
28 daytreatment; thenfollow-up at 1and 3 months
3-month follow-up
5
Motivationalinterviewing
Single 2-hoursession; thenfollow-up at 1and 3 months
3-month follow-up
6
Motivationalincentives (drugfree clinics)
12-week study,with follow-upvisits at 1, 3,and 6 monthsafter enrollment
6-month follow-up
7
Motivationalincentives(methadoneclinics)
12-week study,with follow-upvisits at 1, 3,and 6 monthsafter enrollment
6-month follow-up
9
Smokingcessationtreatment
9-week study,with follow-upvisits at 9, 13,and 26 weeksafter targetsmoking quitdate
13-week follow-up
10
Medication trialfor opioid-dependentadolescents
12-week study,with follow-upvisits at 24, 36,and 52 weeksafter enrollment
12-week end oftreatment
11
Telephone callsupport toincrease post-dischargeengagementand decreasedrug/alcohol use
12-week study,with follow-upvisit at week 13
13-week follow-up
13
Motivationalenhancement inpregnantsubstance users
4-week study,with follow-upvisits at 4 and12 weeks afterstudy
12-week follow-up
15
“Seeking Safety”treatment fortrauma forwomen withPTSD
6-week study,with follow-upvisits at 1 week,3, 6, and 12months aftertreatment
12-month follow-up
18
HIV/STD safersex for men
1 or 5 sessionintervention,with follow-upvisitsimmediately,and 3 and 6months posttreatment
3-month follow-up
19
HIV/STD safersex for women
1 or 5 sessionintervention,with follow-upvisitsimmediately,and 3 and 6months posttreatment
3-month follow-up
21
Motivationalenhancementfor Spanish-speaking clients
3 sessionintervention,with follow-upvisits at 1 and 3months
3-month follow-up
Table 2. Client characteristics by protocol
Table 1. Protocol characteristics
%
Chi-square p-value
Ethnicity
<0.0001
Black
70%
White
62%
Hispanic/other
74%
Gender
0.11
Male
67%
Female
69%
Age
<0.0001
15-19
65%
20-29
64%
30-39
65%
40-49
73%
50-59
74%
60+
69%
Prescription methadone in last30 days
<0.0001
No
64%
Yes
80%
Table 3. Proportion of clients completing study endpoint visit
Table 4. Odds ratios from multivariate logistic regression models,modeling the odds of failing to complete the study endpoint visit
Model 1: Clients on methadone (last 30 days)
OR (95% CI)
p-value
Age (1-year interval)
0.99 (0.97, 1.004)
0.13
Ethnicity
Black
-reference-
White
0.95 (0.59, 1.5)
0.77
Hispanic/other
0.82 (0.49, 1.4)
0.37
Sex (female)
0.83 (0.58, 1.2)
0.31
Length of follow-up (days)
1.001 (0.998, 1.004)
0.37
Model 2: Clients not on methadone
OR (95% CI)
p-value
Age (1-year interval)
0.994 (0.986, 1.002)
0.12
Ethnicity
Black
-reference-
White
1.5 (1.2, 1.9)
<0.0001
Hispanic/other
0.70 (0.55, 0.89)
<0.0001
Sex (female)
0.84 (0.71, 1.004
0.06
Length of follow-up (days)
0.999 (0.998, 1.0)
0.03