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Secondary evaluations of MTA 36-month outcomes: propensity score and growth mixture model analyses
Objective:
To evaluate two hypotheses: that self-selection bias contributed to lack of medication advantage at the 36-month assessment of the Multimodal Treatment Study of Children With ADHD (MTA) and that overall improvement over time obscured treatment effects in subgroups with different outcome trajectories.
Method:
Propensity score analyses, using baseline characteristics and severity of attention-deficit/hyperactivity disorder symptoms at follow-up, established five subgroups (quintiles) based on tendency to take medication at the 36-month assessment. Growth mixture model (GMM) analyses were performed to identify subgroups (classes) with different patterns of outcome over time.
Results:
All five propensity subgroups showed initial advantage of medication that disappeared by the 36-month assessment. GMM analyses identified heterogeneity of trajectories over time and three classes: class 1 (34% of the MTA sample) with initial small improvement followed by gradual improvement that produced significant medication effects; class 2 (52%) with initial large improvement maintained for 3 years and overrepresentation of cases treated with the MTA Medication Algorithm; and class 3 (14%) with initial large improvement followed by deterioration.
Conclusions:
We failed to confirm the self-selection hypothesis. We found suggestive evidence of residual but not current benefits of assigned medication in class 2 and small current benefits of actual treatment with medication in class 1.
Insights
Self-selection bias did not explain the lack of medication advantage in the Multimodal Treatment Study of Children With ADHD (MTA). However, medication showed benefits in specific subgroups over time.
Area of Science:
- Child and Adolescent Psychiatry
- Behavioral Science
- Clinical Psychology
Background:
- The Multimodal Treatment Study of Children With ADHD (MTA) assessed long-term medication effects.
- Previous findings suggested a lack of medication advantage at 36 months.
- Hypotheses included self-selection bias and obscured subgroup treatment effects.
Purpose of the Study:
- To investigate if self-selection bias influenced the MTA study's 36-month outcome.
- To determine if overall improvement masked differential treatment effects in ADHD subgroups.
- To analyze medication adherence and its impact on ADHD symptom trajectories.
Main Methods:
- Propensity score analyses were used to create five subgroups based on medication adherence.
- Growth Mixture Modeling (GMM) identified distinct outcome trajectories over time.
- Baseline characteristics and ADHD symptom severity informed the analyses.
Main Results:
- Initial medication advantages were observed across all propensity score subgroups but diminished by 36 months.
- GMM identified three distinct outcome trajectory classes: gradual improvement (class 1), sustained large improvement (class 2), and initial improvement with deterioration (class 3).
- Class 1 showed significant medication effects, class 2 had overrepresentation of MTA Medication Algorithm use, and class 3 exhibited symptom decline.
Conclusions:
- The self-selection bias hypothesis was not supported.
- Residual benefits of assigned medication were suggested in class 2, with current benefits in class 1.
- Heterogeneity in treatment response and outcome trajectories for ADHD was confirmed.
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