Conceptual Considerations for Analysis of EMA Data
Saul Shiffman, Ph.D.University of Pittsburgh
___Co-Founder, invivodata, inc.
Consult to GlaxoSmithKline
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No Stats
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Self-Report Methods
· Global self-report “Are you the sort of person who…?” “On average….”
· Time-bound recall “In the past month…”
· Episodic recall “When you first used…”
· Momentary assessment
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Ecological Momentary Assessment (EMA)
· Ecological Real-world environments & experience Ecological validity
· Momentary Real-time assessment & focus Avoid recall
· Assessment Self-report, psychophysiology, biological samples Repeated, intensive, longitudinal Allow analysis of process over time
Stone & Shiffman, 1994
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Characteristics of Ecological Momentary Assessment
· Assesses subjects in the natural environment· Assesses phenomena as they occur· Considers assessments to be samples· Gathers many repeated observations
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Sampling Schemes
· Event-based– Record made when event occurs; subject
typically initiates– Event triggers assessment
· Time-based Regular intervals or milestones
– Daily diary; at every meal– Clock or milestone triggers assessment
Time-based schedules controlled by investigator– Random time sampling or other schemes– Need facilities for scheduling and triggering
assessment
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Combined Time & Event SamplingSituational Associations with Smoking
Why Bother?
· Ecological validity To study and understand the real world
· Self-report validity To avoid recall error and bias
· Reliability through aggregation To get many observations to achieve reliability, replication
· Temporal ordering and resolution To study how events and processes unfold over time
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Craving and Smoking…and Craving…
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Time
Cra
ving
Time
Cra
ving
Downward Spiral of Self-Efficacy as Lapses Lead to Relapse
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Time
Sel
f-E
ffic
acy
Time is a Crucial Element in EMA Analysis
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Collapsing Time:Between-Subject Analyses
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Craving reportedby abstinent smokerstreated withnicotine patch vsplacebo
Shiffman, S. & Ferguson, S.G. (2008). The effect of nicotine patch on cigarette craving over the course of the day: Results from two randomized clinical trials. Current Medical Research and Opinion, 24, 2795-2804
Blenderizing Time:Between-Occasion Analyses
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% of occasions w/ alcohol consumption,when smoking vsnot smoking,among non-dailysmokers identified as“social smokers”
Shiffman, S., Li, X., Dunbar, M., Scholl, S., & Tindle, H. (2012, March). Non-daily smokers = Social smokers? In a symposium on Increasing our understanding of nondaily smoking: Individual patterns, smoking trajectories, and cultural influences (Jasjit Ahluwalia & Saul Shiffman, chairs), presented at the annual meeting of the Society for Research on Nicotine and Tobacco (SRNT), Houston, TX
THURSDAY 1:00 p.m.–2:30 p.m.........Grand Ballroom C, Level 4 INCREASING OUR UNDERSTANDING OF NONDAILY SMOKING
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PromptedAssessment
SubjectEntries
R ***
T L
PrecedingDay
LapseDay
SucceedingDay
R - Random Prompt T - TemptationL - Lapse
Time as Sequence
within subject
Negative Affect in Background, Temptations & First Lapses
Series10
25
50
75
100
125
150
Random
Tempts
Lapses
Neg
ativ
e A
ffec
t (T
sco
re)
Shiffman, S., Paty, J.A., Gnys, M., Kassel, J.D., & Hickcox, M. (1996). First lapses to smoking: Within-subjects analyses of real-time reports. Journal of Consulting and Clinical Psychology, 64, 366-379
Pre-Post Event
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Self-Efficacy,before and after a Temptation vsa Lapse episode
Shiffman, S., Hickcox, M., Paty, J.A., Gnys, M., Kassel, J.D., & Richards, T. (1997). The Abstinence Violation Effect following smoking lapses and temptations. Cognitive Therapy and Research, 21 (5), 497-523
Event-Anchored Calendar
Time
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Craving intensity amongabstinent smokers,temptation episodes vsrandom moments, over days since quitting
Shiffman, S., Engberg, J., Paty, J.A., Perz, W., Gnys, M., Kassel, J.D., & Hickcox, M. (1997). A day at a time: Predicting smoking lapse from daily urge. Journal of Abnormal Psychology, 106, 104-116
Event-Anchored ReverseCalendar & Clock Time
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Negative affectamong abstinentsmokers, in the days and hours preceding a first lapse, by lapse trigger
Shiffman, S. & Waters, A. J. (2004). Negative affect and smoking lapses: A prospective analysis. Journal of Consulting and Clinical Psychology, 72 (2), 192-201
Time as Risk
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Time to relapse, after a first lapse, by pleasantness ofsmoking in the lapse
Shiffman, S., Hickcox, M., Paty, J.A., Gnys, M., Kassel, J.D., & Richards, T. (1996). Progression from a smoking lapse to relapse: Prediction from abstinence violation effects and nicotine dependence. Journal of Consulting and Clinical Psychology, 64, 993-1002
Repeated Events over Time
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Accelerating time-to-re - lapse times oversuccessive lapses,initially slowed bynicotine patch treatment
Kirchner, T.R., Shiffman, S., Wileyto, P. (2012). Relapse dynamics during smoking cessation: Recurrent abstinence violation effects and lapse-relapse progression. Journal of Abnormal Psychology, 121, 187-197
Even More Ways to Think About Time in EMA Data
· Reciprocal effects e.g., smoking reduces self-efficacy, which increases
smoking, which reduces self-efficacy, which …..
· Cumulative effects e.g., cumulative effort of coping eventually exhausts
quitters, leading to relapse
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Data Analysis
· Effort: 50% thinking about theory and question 30% organizing data to address question 20% statistical analysis (now easier)
· Design envy: Experiments: structure dictates analyses EMA: Not much structure… Question dictates
analysis
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5 Subjects’ EMA Data
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5 Subjects’ EMA Data
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304 Subjects’ EMA Data
29N=304 subjects, 191,841 observations
Design Envy
· In traditional design, design dictates analysis· 1 or n observations / person· Confounds are limited by design
· EMA: We have to work harder to select, arrange, structure data to fit question & analysis
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Active Placebo
Men
Women
Summary
· EMA data unstructured+ Can address many different questions
- Require hard thinking & effort to shape for analysis
· Find structure and statistics to match question(not vice versa)
· Consider treatment of time in analysis
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