Identifying treatment effects using trimmed means when data are missing not at random

Testing treatment effects in repeated measures designs: Trimmed means and bootstrapping

British Journal of Mathematical and Statistical Psychology ◽

10.1348/000711000159286 ◽

2000 ◽

Vol 53 (2) ◽

pp. 175-191 ◽

Cited By ~ 20

Author(s):

H. J. Keselman ◽

Rhonda K. Kowalchuk ◽

James Algina ◽

Lisa M. Lix ◽

Rand R. Wilcox

Keyword(s):

Repeated Measures ◽

Treatment Effects ◽

Repeated Measures Designs ◽

Trimmed Means

Download Full-text

Sensitivity to missing not at random dropout in clinical trials: use and interpretation of the Trimmed Means Estimator

10.1101/2021.03.05.21252334 ◽

2021 ◽

Author(s):

Audinga-Dea Hazewinkel ◽

Jack Bowden ◽

Kaitlin H. Wade ◽

Tom Palmer ◽

Nicola Wiles ◽

...

Keyword(s):

Sensitivity Analysis ◽

Treatment Effect ◽

Missing Values ◽

Behavioural Therapy ◽

Drop Out ◽

Sensitivity Analyses ◽

Missing Not At Random ◽

Cognitive Behavioural ◽

Location Shift ◽

Trimmed Means

AbstractOutcome values in randomized controlled trials (RCTs) may be missing not at random (MNAR), if patients with extreme outcome values are more likely to drop out (e.g., due to perceived ineffectiveness of treatment, or adverse effects). In such scenarios, estimates from complete case analysis (CCA) and multiple imputation (MI) will be biased. The trimmed means (TM) estimator operates by setting missing values to the most extreme value, and then “trimming” away equal fractions of both treatment groups, estimating the treatment effect using the remaining data. The TM estimator relies on two assumptions, which we term the “strong MNAR” and “location shift” assumptions. In this article, we derive formulae for the bias resulting from the violation of these assumptions for normally distributed outcomes. We propose an adjusted estimator, which relaxes the location shift assumption and detail how our bias formulae can be used to establish the direction of bias of CCA, MI and TM estimates under a range of plausible data scenarios, to inform sensitivity analyses. The TM approach is illustrated with simulations and in a sensitivity analysis of the CoBalT RCT of cognitive behavioural therapy (CBT) in 469 individuals with 46 months follow-up. Results were consistent with a beneficial CBT treatment effect. The MI estimates are closer to the null than the CCA estimate, whereas the TM estimate was further from the null. We propose using the TM estimator as a sensitivity analysis for data where it is suspected that extreme outcome values are missing.

Download Full-text

A Phonomotor Approach to Apraxia of Speech Treatment

American Journal of Speech-Language Pathology ◽

10.1044/2020_ajslp-19-00116 ◽

2020 ◽

Vol 29 (4) ◽

pp. 2109-2130

Author(s):

Lauren Bislick

Keyword(s):

Phase I ◽

Treatment Effects ◽

Single Case ◽

Motor Planning ◽

The Other ◽

Multimodal Approach ◽

Apraxia Of Speech ◽

Duration Of Treatment ◽

Treatment Gains ◽

Future Work

Purpose This study continued Phase I investigation of a modified Phonomotor Treatment (PMT) Program on motor planning in two individuals with apraxia of speech (AOS) and aphasia and, with support from prior work, refined Phase I methodology for treatment intensity and duration, a measure of communicative participation, and the use of effect size benchmarks specific to AOS. Method A single-case experimental design with multiple baselines across behaviors and participants was used to examine acquisition, generalization, and maintenance of treatment effects 8–10 weeks posttreatment. Treatment was distributed 3 days a week, and duration of treatment was specific to each participant (criterion based). Experimental stimuli consisted of target sounds or clusters embedded nonwords and real words, specific to each participants' deficit. Results Findings show improved repetition accuracy for targets in trained nonwords, generalization to targets in untrained nonwords and real words, and maintenance of treatment effects at 10 weeks posttreatment for one participant and more variable outcomes for the other participant. Conclusions Results indicate that a modified version of PMT can promote generalization and maintenance of treatment gains for trained speech targets via a multimodal approach emphasizing repeated exposure and practice. While these results are promising, the frequent co-occurrence of AOS and aphasia warrants a treatment that addresses both motor planning and linguistic deficits. Thus, the application of traditional PMT with participant-specific modifications for AOS embedded into the treatment program may be a more effective approach. Future work will continue to examine and maximize improvements in motor planning, while also treating anomia in aphasia.

Download Full-text