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Recent Advances in Latent Variable Modeling
Bengt Muthen
[email protected]: www.statmodel.com
Presentation at the joint Stats/RMME colloquium, UCONNNovember 20, 2020
I thank Tihomir Asparouhov for comments and Noah Hastings for assistance.
Bengt Muthen Advances in Latent Variable Modeling 1/ 47
Overview
Many different models with a common theme - longitudinal analysis:
Modeling ideas of multilevel factor analysis and longitudinalstructural equation modeling
Latent transition analysis
Multilevel time series analysis
Bayesian analysis of count, nominal, and binary logit outcomes
Drawing on material in Mplus Web Talks atwww.statmodel.com
Bengt Muthen Advances in Latent Variable Modeling 2/ 47
Multilevel Factor Analysis Origins
Yij = ν +YBj +YWij (1)
= ν +ΛB fBj + εBj︸ ︷︷ ︸+ΛW fWij + εWij︸ ︷︷ ︸, (2)
with covariance structure V(Yij) = ΣB +ΣW where each covariancematrix has a factor model structure, Λ Ψ Λ′+Θ.
Cronbach (1976). Research on classrooms and schools: Formulation ofquestions, design, and analysis. Stanford University, School of Ed
Harnqvist (1978). Primary mental abilities of collective and individuallevels. Journal of Educational Psychology
Goldstein & McDonald (1988). A general model for the analysis ofmultilevel data. Psychometrika
McDonald & Goldstein (1989). Balanced versus unbalanced designsfor linear structural relations in two-level data. British Journal ofMathematical and Statistical Psychology
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Random Intercept View of Two-Level Factor Analysis
The two-level factor analysis model (one factor on each level),
yij = ν +λB fBj + εBj + λW fWij + εWij
expressed in terms of level 1 and level 2 (within and between),
Level 1 : yij = νj +λW fWij + εWij ,
Level 2 : νj = ν +λB fBj + εBj .
Two key aspects:Two-level factor analysis can be viewed as a random interceptmodel where the intercepts have a factor structureBecause the random intercepts appear for the factor indicators y,measurement non-invariance is allowed
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Two-Level Factor Analysis in a Model Diagram
A random intercept is represented in model diagrams as a factor(latent variable) with unit loading (slope) for the observedoutcomeE.g. students within classrooms or schools. Achievement testing
Typically fewer between-level factors than within-level factorsfb interpretation different from fw interpretation
Within
Between
fb
y1 y6
fw1 fw2
y6
y2 y3 y4 y5
y1 y2 y3 y4 y5
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Going Deeper Into Multilevel Factor Analysis
Within
Between
fb
fw
y1 y2 y3
Cross-sectional: Students within schools
But the case of time points nested within individuals is also multilevel -so why not apply this model to longitudinal data?
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What Multilevel Factor Modeling Can Teach UsAbout Single-Level Modeling: Longitudinal Model for T=2
==
=u11 u12 u13 u u u21 22 23
fw1 fw2
fb
u1 u2 u3
Within
Between
fb
u1 u2 u3
fw
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Longitudinal Factor Analysis
Hamaker et al. (2016). Using a few snapshots to distinguish mountainsfrom waves: Weak factorial invariance in the context of trait-stateresearch. Multivariate Behavioral Research. - “CUTS” (Common andUnique Trait State) model, based on multilevel FA
Argues that factors obtained from cross-sectional factor analysis arepartly determined by between- and partly by within-person covariancestructure (Cattell, 1978): “An uninterpretable blend” (R & B, 2002)
Multilevel-based longitudinal factor analysis allows differencesbetween between-person, trait-like factor structure and within-person,state-like factor structure
T=2 is sufficient to determine the within-person factor structure. Noneed for intensive longitudinal data to estimate a factor model for eachperson (N=1 analysis; Cattell’s P-technique)
Relates to latent state-trait work in Marsh-Grayson (1994) in SEM, Eid(1996) in MPRO, Dumenci-Windle (1996) in MBR, Geiser-Lockhart(2012) in Psych Methods, Geiser et al. (2015) in Behav Res, andGeiser (2020): Longitudinal Structural Equation Modeling with MplusA Latent State-Trait Perspective. Guilford Press.
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Longitudinal Factor AnalysisBased on Multilevel Thinking
==
=u11 u12 u13 u u u21 22 23
fw1 fw2
fb
u1 u2 u3
Model extended to include auto-regression for the fw factors
Corresponds to a cross-sectional model where students within schoolsinfluence each other
This multilevel-based longitudinal model is quite different from the”naive” longitudinal model which uses only the bottom part
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46 Years Ago: University of Wisconsin - Madison 1974-75
Wheaton, B., Muthen, B.,Alwin, D., & Summers, G.(1977). Assessing reliabilityand stability in panel models.In D. R. Heise (Ed.),Sociological Methodology1977 (pp. 84 - 136). SanFrancisco: Jossey-Bass, Inc.
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“Wheaton et al” 1977 Structural Equation Model of theStability of Alienation 1996-1971
a1 p1 a2 a3p2 p3
ses
f1 f2 f3
ed sei
Anomia and Powerlessness as indicators of alienation
Interest in stability estimates 1966 to 1967 and 1967 to 1971 whiletaking measurement error into account
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A Random Intercept Version of the “Wheaton et al” Model
a p
ses
ed sei
a1 p1 a2 a3p2 p3
f1 f2 f3
WithinBetween
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Random Intercept Model Features
a p
ses
ed sei
a1 p1 a2 a3p2 p3
f1 f2 f3
WithinBetween
Still a single-level, wide model
Two random intercepts representing ”between-level” variation(stable over time) instead of many correlated residuals
SES is a ”between-level” variable (does not change over time)and influences only the random intercepts
The relationships between the factors over time representwithin-person dynamics
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Model Fit Results: Classic vs New (N = 932)
Model # par’s logL BIC Chi-2 df p RMSEA CFI
Classic 31 -19455 39121 90.04 13 0.00 0.080 0.979New 25 -19425 39021 30.65 19 0.04 0.026 0.997
Findings for the New, Random Intercept model:Despite using fewer parameters (25 vs 31), it has better logL,better BIC, and better chi-square, RMSEA, and CFIOn Level-2 (Between), SES has a significant negative effect onthe random intercepts as expected. This means that SES explainsmeasurement non-invariance across peopleOn level-1 (Within), Positive effect of f1 on f2 (1966 to 1967) butno significant effect of f2 on f3 (1967 to 1971)
Some across-time equalities can be relaxed for even better fit
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Overview
Modeling ideas of multilevel factor analysis and longitudinalstructural equation modeling
Latent transition analysisMultilevel time series analysis
Bayesian analysis of count, nominal, and binary logit outcomes
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Hidden Markov - Latent Transition Analysis
u: observed categorical variable (latent class indicator)c: latent categorical variable (latent class variable)
u1 u3u2
c1 c2 c3
u4
c4
u5
c5
u11
c1 c2 c3
u12 u31 u32u21 u22
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LTA Features
u11
c1 c2 c3
u12 u31 u32u21 u22
1 Measurement probabilities: P(Ut|Ct) - LCA for each time point,measurement invariance across time
2 Initial status probabilities: P(C1)
3 Transition probabilities: P(C2|C1), P(C3|C2)
Extensions:
Covariates: Influencing latent class probabilities and transitionprobabilities
Multiple-group analysis: Measurement invariance
Mover-Stayer modeling
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What’s Missing in These Models? Random Intercepts
u1 u3u2
c1 c2 c3
u4
c4
u5
c5
u11
c1 c2 c3
u12 u31 u32u21 u22
Single indicator per time pointA statistical perspective
Multilevel modeling: Level 1 = time, level 2 = subjectRandom effects, especially random intercepts
A substantive perspectiveTrait theory in psychologyBetween-subject differences that are stable over time
Multiple indicators per time pointA psychometric perspective
Measurement non-invarianceMultilevel factor analysisMultilevel latent class analysis
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Hidden Markov Modeling with a Random Intercept
u
1 1 1
u1 u2 u3
c1 c2 c3
Altman (2007). Mixed hidden Markov models. Journal of the AmericanStatistical Association, 102, 201-210.
Relapsing-remitting multiple sclerosis patients, N=39
Symptoms worsen and then improve in alternating periods ofrelapse and remission
Outcome: Number of lesions in the brain (count variable)
T=24 (monthly scans for two years)
2 latent classes (hidden states): Relapse versus remission
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Single-Indicator LTA (Hidden Markov)
u
1 1 1
u1 u2 u3 u1 u2 u3
c1 c2 c3 c1 c2 c3
The Hidden Markov model on the left can use the fastbackward-forward Baum-Welch algorithm for ML estimation
The random intercept model on the right loses this simplicity - the U’sare no longer independent conditional on the Cs
ML estimation needs numerical integration with much heaviercomputationsBartolucci et al. (2012). Latent Markov Models for LongitudinalData
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Random Intercept LTA (RI-LTA)
u11
c1 c2 c3
u12 u31 u32u21 u22
f
λ1 λ1 λ1 λ2λ2λ2
Muthen & Asparouhov (2020). Random intercept latent transitionanalysis (RI-LTA). Forthcoming in Psychological Methods.
Papers and Mplus scripts:http://www.statmodel.com/RI-LTA.shtml
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Mplus Software Improvements for LTA and RI-LTA
RI-LTA can be time consuming due to numerical integration andneeding many random starts to find the global maximum.Mplus Version 8.4 released last year:
Significant speed improvements for computationally demandingmixture models such as with LTA and RI-LTA using a new three-stagerandom starts search and using specialized algorithms drawing onBaum-Welch ideas
Asparouhov & Muthen (2019). Random Starting Values andMultistage Optimization (Technical Report: http://www.statmodel.com/download/StartsUpdate.pdf)
”A 20 hours computation in Mplus 8.3 can be done in Mplus 8.4in less than 15 minutes, by utilizing the advantages of thethree-stage estimation, the Baum-Welch algorithm, as well asupdated hardware (i9-9900k Intel CPU)”
Substantially simplified output for mixture models with multiple latentclass variables
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Regular LTA Fits Worse than RI-LTA Most of the Time
Analyses of 4 data sets from the LTA literature (data athttp://www.statmodel.com/RI-LTA.shtml):Table 1: Model fitting results
Life Satisfaction (non-stationary) Mood (stationary)N=5147, T=5, R=1, J=5 N=494, T=4, R=2, J=2
Model # par’s logL BIC Model # par’s logL BIC
Regular LTA 11 -15326 30745 Regular LTA 7 -2053 4150
RI-LTA 12 -15267 30637 RI-LTA 9 -2018 4093
Reading proficiency (non-stationary) Dating and sexual risk behavior (stationary)N=3574, T=4, R=5, J=3 N=2933, T=3, R=3, J=5
Regular LTA 35 -21793 43873 Regular LTA 49 -16202 32796
RI-LTA 40 -20329 40985 RI-LTA 52 -16043 32502
1
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Reading Proficiency. Kaplan (2008)
Early Childhood Longitudinal Study (ECLS-K), N = 3574
4 time points: Fall and Spring of Kindergarten and Fall and Spring ofGrade 1
5 binary items representing mastery of:
Basic reading skills of letter recognitionBeginning soundsEnding letter soundsSight wordsWords in context
3 latent classes corresponding to 3 stages of learning:
Low alphabet knowledge, early word reading, early readingcomprehension
Kaplan (2008). An overview of Markov chain methods for the study ofstage-sequential developmental processes. Developmental Psychology
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Reading Data Latent Class Probabilities
Regular LTA
Fall K Spring K Fall 1st Spring 1st
ClassProbabilities
1 0.694 0.235 0.142 0.0412 0.284 0.635 0.627 0.1543 0.023 0.130 0.232 0.805
RI-LTA
Fall K Spring K Fall 1st Spring 1st
ClassProbabilities
1 0.948 0.161 0.040 0.0102 0.049 0.818 0.880 0.0173 0.003 0.022 0.080 0.973
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Reading Data Transition Probabilities
Regular LTA
1 2 3
TransitionProbabilities Fall K -– Spring K
1 0.338 0.649 0.0122 0.001 0.652 0.3483 0.000 0.000 1.000
RI-LTA
1 2 3
TransitionProbabilities Fall K -– Spring K
1 0.170 0.820 0.0102 0.000 0.819 0.1813 0.000 0.000 1.000
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Transition Probabilities Influenced By Covariate: RI-LTA
u11
c1 c2 c3
u12 u31 u32u21 u22
f
x
Mplus Web Talk No. 2 at www.statmodel.com
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Overview
Modeling ideas of multilevel factor analysis and longitudinalstructural equation modeling
Latent transition analysis
Multilevel time series analysisBayesian analysis of count, nominal, and binary logit outcomes
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What Single-Level Modeling Can Teach UsAbout Multi-Level Modeling
u11
c1 c2 c3
u12 u31 u32u21 u22
f
λ1 λ1 λ1 λ2λ2λ2
How do you do analyze relations between variables at different timepoints using two-level modeling?
Multilevel time series analysis (time and individual)Other random effects can be added: Random slopes, randomvariances, random AR, random transition probabilitiesMany time points required - intensive longitudinal data (EMA,ESM, daily diary)
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Dynamic Structural Equation Modeling (DSEM)
Single-level, wide Two-level, long, time series (DSEM)
u11
c1 c2 c3
u12 u31 u32u21 u22
f
λ1 λ1 λ1 λ2λ2λ2
Within (time)
u1 u2
f
λ λ
ct-1 ct
u1t u2t
Between (subject)
1 2
DSEM data are in long format:2 outcomes per time point results in 2 columns of data (not 2*T)
Across-time effects specified by using lags: C ON C&1 (lag 1)Bengt Muthen Advances in Latent Variable Modeling 30/ 47
Dynamic Structural Equation Modeling (DSEM)
Two-level analysis: randomeffects varying across subjectsCross-classified analysis (oftime and subject): randomeffects varying across subjectsand time
fb φ
Between
φfwtfwt-1
Within
DSEM using Bayesian analysis:
Asparouhov, Hamaker & Muthen (2017). Dynamic Latent ClassAnalysis. Structural Equation Modeling: A MultidisciplinaryJournal, 24:2, 257-269Asparouhov, Hamaker & Muthen (2018). Dynamic structuralequation models. Structural Equation Modeling: AMultidisciplinary Journal, 25:3, 359-388
Papers at http://www.statmodel.com/TimeSeries.shtml
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Bayesian Analysis: Advantages over ML
Bayes with non-informative priors - a powerful computingalgorithm :
Analyses are often less computationally demanding, for example,when maximum-likelihood requires high-dimensional numericalintegration due to many latent variables (factors, random effects)In cases where maximum-likelihood computations areprohibitive, Bayes with non-informative priors can be viewed as acomputing algorithm that would give essentially the same resultsas maximum-likelihood if maximum-likelihood estimation werecomputationally feasible
New types of models can be analyzed where themaximum-likelihood approach is not feasible (e.g. multilevel timeseries models with many random effects)
Bayes with informative parameter priors - a better reflection ofhypotheses based on previous studies
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Random Effects in Two-Level Time Series Modeling
Time nested in level 2 units (persons, firms, etc)Random effects allowing parameter variation across level 2units:
Random intercept (level)Random slopes on covariates such as timeRandom varianceRandom auto-regressionRandom amplitude
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Modeling Cycles: Dummies, Splines, Sine-Cosine
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5
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Time
-7 -6.5
-6 -5.5
-5 -4.5
-4 -3.5
-3 -2.5
-2 -1.5
-1 -0.5
0 0.5
1 1.5
2 2.5
3 3.5
4 4.5
5
B2a_
Y, m
ean
= 24 hrs
Biological cycles24-hour cycles: Circadian rhythm such as heart rate
Behavioral cyclesWeekly drinking pattern
Environmental cyclesMonthly temperature fluctuations
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Cyclic Formulas Using Sine-Cosine
f (t) = A cos (2π ω t+φ)
=−A sin φ︸ ︷︷ ︸β1
sin (2π ω t)︸ ︷︷ ︸x1
+A cos φ︸ ︷︷ ︸β2
cos (2π ω t)︸ ︷︷ ︸x2
Amplitude = A =√
β 21 +β 2
2
Phase = φ = tan−1(−β1/β2)
ω is a frequency index defined as cycles per unit. Usingω = 1/24 = 0.04167 gives 24-hour cycles
Multiple f (t) components with different cycles per unit can beused. Spectral analysis finds the components of the cycles
Two-level or cross-classified analysis with random effects
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Very Long Longitudinal Data: T= 1096
Electricity consumption of firms measured daily (and hourly)over 3 years: T=1096 (Schultzberg, 2018)
Intervention: change in tariffN=184 intervention group (N= 800 Control group; not used here)Pre-intervention data for 1 year, post-intervention data for 2 yearsSine-cosine cross-classified model
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ean
B2a_Y1, mean (autocorr = 0.910(0.030))
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ean
B2a_Y2, mean (autocorr = 0.821(0.030))
In the left part of the figure, the curve after the intervention(marked by a vertical line) shows the predicted development inthe absence of the intervention
In the right part of the figure, significant drop in amplitude afterthe intervention (marked by a vertical line)
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Intervention Modeling in Multilevel Time Series Analysis:Propensity Score Analysis
No randomization: Matching on propensity scores obtained frompre-intervention random effects to evaluate post-interventionoutcomes
Schultzberg (2019). Using high-frequency pre-treatmentoutcomes to identify causal effects in non-experimental data
Within (time)
Between (firms)
tx
yt yt-1
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Very Long Longitudinal Data
Schultzberg & Muthen (2018). Number of subjects and time pointsneeded for multilevel time series analysis: A simulation study ofdynamic structural equation modeling. Structural Equation Modeling.25:4, 495-515
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Intervention Modeling in Multilevel Time Series Analysis:Randomized Studies
Intervention interacting with pre-intervention random effects ininfluencing post-intervention random effects (for whom is theintervention effective?)
Within
Between
yt-1pre yt
pre yt-1post yt
post
tx
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Randomized Trial
Geschwind et al. (2011). Mindfulness training increases momentarypositive emotions and reward experience in adults vulnerable todepression: A randomized controlled trial. Journal of Consulting andClinical Psychology
Experience sampling method (ESM): T= 60 pre, 60 post (each periodhas 10 beeps/day via digital wristwatch for 6 days), N=119
Muthen et al. (2020). In preparation: DSEM with daily cycles inpositive affect modeled by sine-cosine curve with random effects
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Randomized Trial DSEM Results
Within
Between
yt-1pre yt
pre yt-1post yt
post
tx
Preliminary findings for intervention effects on the random effects ofthe post-intervention time series for momentary positive emotions:
Positive effect on level (intercept); higher effect on level forpersons with higher pre-intervention levelPositive effect on level for persons with high pre-interventionauto correlation
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Overview
Modeling ideas of multilevel factor analysis and longitudinalstructural equation modeling
Latent transition analysis
Multilevel time series analysis
Bayesian analysis of count, nominal, and binary logitoutcomes
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Bayesian Analysis of Count, Nominal,and Binary Logit Outcomes
”...has long been recognized as a hard problem”Polson, Scott, Windle (2013). Bayesian inference for logisticmodels using Polya-Gamma latent variables. JASA
Asparouhov, Muthen (2020). Expanding the Bayesian structuralequation, multilevel and mixture models to logit,negative-binomial and nominal variables
Allows many latent variables (factors, random effects) in ageneral modeling frameworkCount modeling using negative binomial (NB-2) and PoissonMplus Version 8.5 released earlier this week
Polson et al. (2013) considered an autoregressive N=1 timeseries model for count data
Asparouhov-Muthen (2020) consider multilevel (N > 1) versions
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Application to Longitudinal Count Modeling
Example with T=10: Maximum-likelihood estimation requires11 dimensions of integration; intractable. Bayes ok at N ≥ 500
ν
η1 η2 η10
y1 y2 y10...
...
Yit ∼ NB2(νi +ηit,α) (3)
νi ∼ N(ν ,v1) (4)
ηit = ρηi,t−1 + εit, for t = 2, ...,T (5)
εit ∼ N(0,v2). (6)
The model has 5 Negbin parameters: ν (random intercept mean),ρ (AR), α (dispersion), v1 and v2 (variance/residual variance)
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Random Intercept Cross-Lagged Panel Model (RI-CLPM)
Extensions of Hamaker et al. (2015) to counts and categoricaloutcomes (in preparation)
z1
y1
wy1
wz1
y
z
z3
y3
wy3
wz3
z2
y2
wy2
wz2
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UCONN 1995 Origins: Traits, States, and Errors
Kenny & Zautra (1995). The trait-state-error model for multiwavedata. Journal of Consulting and Clinical Psychology
TRAIT-STATE-ERROR MODEL 55
e.
Figure 2. Bivariate trait-state-error model. Paths from state factors (a, b, c, and d) are denoted as ax
Oyx, axy, and ayy in the text. Numerals 1 through 4 indicate the four lags; e = error; u = disturbance.
1989). For four-wave data, the resulting model with both ofthese modifications would have zero degrees of freedom be-cause an additional six degree parameters (three error variancesand three loadings) are estimated. Such a model is just-identi-fied and there is no chi-square test.
Bivariate Model
The major interest in this article is the causal relationshipbetween two variables. There are two variables, X and Y, eachof which is measured at each wave. Both X and /are assumedto be caused by a trait, Tx or Ty, a state factor, Sx or Sy, and bymeasurement error, Ex or Ey. So we have
X = Tx + Sx + Ex and
Y= Ty + Sy + Ey.
For each variable, there are the four parameters described in theprevious section: trait variance V( Tx) and V( Ty); state distur-bance variance V(UX) and V(Uy)', error variance V(EX) andV(Ey); and two autoregressive parameters (a^) and (ayy).There are five additional bivariate parameters or parametersthat describe the association between X and Y. The first threeinvolve correlations between the X and Y variables at the traitC( Tx, Ty), state C( Ux, Uy), and error C(EX, Ey) levels. Thenext two are lag-1 regression coefficients of state variables: theeffect of Y on X (axy) and the effect of X on Y (ayx). There are atotal of 13 parameters, and the model's degrees of freedom aren(2n+ 1) — 13, where n is the number of waves. The model ispresented in pictorial form in Figure 2.
In principle, one could allow for lag-2 effects; that is, one'scurrent standing is affected by the previous time and the time
before that. This article does not explore this complexity be-cause it seems theoretically unlikely.
There are three nonlinear constraints on the parameters.Each state variance at Time 1 equals the disturbance varianceof the state divided by 1 minus the multiple correlation squaredof the state factor. The state covariance at Time 1 equals a func-tion of the covariance of the state disturbances and the lag co-efficients.3 A practical estimation strategy is to re-estimate themodel and constrain the parameters to their value in the previ-ous solution. The estimation stops when the parameters do notchange very much.
Covariates
If there are covariates that operate at the trait level (e.g., gen-der or ethnicity), their correlation can be estimated and testedat that level. Although one could introduce them into the struc-tural equation model, there is another alternative. One firstcomputes the mean score for each variable (Xand Y) across then time points. One then correlates a covariate with this meanscore. However, this correlation is attenuated because of the factthat the mean score estimates but does not equal the trait factor.To disattenuate the correlation, one multiplies the previous cor-relation by the trait standard deviation (taken from the struc-tural equation model run) divided by the standard deviation ofthe mean of the measures. (This ratio of standard deviationsequals the square root of the reliability of mean score.)
3 That function is as follows:
c- x _ a»fl*yV(Ux) + • y) + C( U*,
Figure 2. The bivariate case
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Recent Paperswww.statmodel.com/recentpapers.shtml
Asparouhov & Muthen (2019). Nesting and equivalence testing for structural equationmodels. Structural Equation Modeling
Asparouhov & Muthen (2019). Random starting values and multistage optimization(Technical Report)
Asparouhov & Muthen (2019). Bayes parallel computation: Choosing the number ofprocessors (Technical Report)
Asparouhov & Muthen (2019). Bayesian estimation of single and multilevel models withlatent variable interactions. Structural Equation Modeling
Asparouhov & Muthen (2019). Advances in Bayesian model fit evaluation for structuralequation models. Structural Equation Modeling
Asparouhov & Muthen (2019). Latent variable centering of predictors and mediators inmultilevel and time-series models. Structural Equation Modeling
Asparouhov & Muthen (2020). Comparison of models for the analysis of intensivelongitudinal data. Structural Equation Modeling
Asparouhov & Muthen (2020). Expanding the Bayesian structural equation, multileveland mixture models to logit, negative-binomial and nominal variables
Hamaker & Muthen (2020). The fixed versus random effects debate and how it relates tocentering in multilevel modeling. Psychological Methods
Muthen & Asparouhov (2020). Latent transition analysis with random intercepts(RI-LTA). Forthcoming in Psychological Methods
Bengt Muthen Advances in Latent Variable Modeling 47/ 47