This document describes MELODEM, an initiative to harmonize analytic approaches across longitudinal dementia studies. It discusses organizing working groups around topics like selection bias, measurement, and time scales. The goals are to conceptually and empirically compare methods, reach consensus on preferred methods, and address barriers to adoption. Working groups meet monthly by phone and annually in person. Papers have been submitted on reporting standards and the sensitivity of findings to practice effects specifications, with others in progress on survival bias and high-dimensional data methods.

1. MELODEM: MEthods in LOngitudinal
DEMentia Research
• Initiative to harmonize analytic approaches across
studies, organized around working groups
• Selection: enrollment, attrition, and survival
• Measurement: retest effects, reliability, validity (scaling)
• Time scales: age vs years of follow-up, survival models
• Time-varying exposures and confounding
• High dimensional data: e.g., neuroimaging, genetics,
geospatial
• Compare methods conceptually and empirically
(across data sets)
• Consensus on preferred methods, considering
current and future data availability
• Identifying barriers to adoption (e.g., software
availability)
1

2. MELODEM: Structure
• 5 Working groups include a group of interested
people participating in the conversation and a core
group of people pushing papers forward.
• Meet approximately monthly via phone
• Annual meetings (2 so far) sponsored by
Fondacion Plan Alzheimer’s
• Discuss progress of the groups and present related
methodological work
• Brings together neurologists, epidemiologists,
biostatisticians, neuropsychologists for “lively”
discussion.
• Interim meetings at relevant conferences e.g.,
ICAD, GSA (?)
2

3. MELODEM: Progress
• Paper submitted summarizing major challenges,
why they are especially salient for dementia
research, and recommendations for transparent
reporting (not for specific analytic approaches)
• Paper drafted on sensitivity of research findings to
practice effects specification (Vivot, Power, et al)
• Papers in progress on survival bias and competing
risk corrections, including a simulation platform to
compare alternative approaches
3

4. MELODEM: Checklist
• Dropout: Describe dropout and correlation of dropout with exposure and past cognitive
history. Specify how potential dropout bias was handled.
• Survival: Describe survival and correlation of survival with exposure and past cognitive
history. Specify how potential survival bias was handled.
• Selective Study Participation: Describe pattern and how handled in analyses.
• Practice effects: Describe evidence of practice effects, how potential practice effects
were handled in the analysis, and sensitivity of results to modeling choice.
• Reliability: Estimate or describe the reliability of the primary outcome measure.
• Unequal interval scaling: show the distribution of the primary outcome measure,
describe any evidence on interval scaling, including ceiling and floor effects.
• Defining time scale: Specify and justify the time scale used. Whatever the time scale,
adjust the analysis for age at a given time (e.g., age at entry).
• Nonlinear cognitive trajectory: Explore the possibility of a nonlinear cognitive decline.
• Time-varying exposures: Justify choice of timing of exposures and confounders used in
analyses.
• Time-varying confounding: Assess whether confounders partially mediate effects.
4