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

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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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