The Gene'c Heritability of Social and Poli'cal Traits: Introduc'on to Twin Studies Levi Li=vay Research and Methods Symposium – WSU January 28, 2010
What is the Central European University? • In Budapest, Hungary (since 1991) • US (and now also EU) accredita'on • Working language: English (strictly) • Only social sciences • Only grad school (MA, PhD, LLM) • One year MA in Poli'cal Science • Diverse Student Body • Big fat endowment by George Soros (read: Lots of Scholarships) • Send us good students!
Step #1: AdmiYng You Have a Problem Predic'ng turnout What do we see here? (beyond chaos?) 33 Independent Variables R 2 = 0.32 Plutzer (APSR 2002
Two Dogmas of Poli'cal Science • Behaviorist Approach – Because internal mental processes and personal preferences cannot be observed, we will focus our inquiry on observed behaviors and revealed preferences. • Ra'onal Choice Theory – Human behavior is best explained by assuming that individuals are ra'onally trying to maximize their individual u'lity. This Slide and the Previous Slide “Stolen” from Darren Schreiber
Model of Individual Behavior: Ra'onal U'lity Maximiza'on • Maximiza'on: we want MORE! (preferences) • Expected behavior can be modeled. • What Is U'lity? • Hard vs. Sod Ra'onal Choice
2002 Nobel Prize Winners: For Work in Experimental Economics Daniel Kahneman Vernon Smith
Solu'ons: “as if” • People might not act ra'onally but… Models work in the aggregate “as if… • Not interested in “as if” aggregate models
Solu'on: “U'lity Is Not Money” Pres'ge Friendship Being Nice Love Sex Power Goods Services Fairness Happiness Gold Jewelry Shopping Accomplishment Family Health Food Clothes Pets Kids Pizza Beer Wine Some'mes This Some'mes That Alcohol Coca~Cola Music Yeah etc. TAUTOLOGY
Search for preferences • Need a new theory to understand and predict preference structures. or • Need a new theory of behavior. • Unselfish Behavior (Altruism) Literature: – Evolu'onary Explana'ons
APSR: May 2005 Cover Ar'cle “…gene'cs play an important role in shaping poli*cal a-tudes and ideologies but a more modest role in forming party iden*fica*on …”
Twin Data • Most informative family data is twin data • Two types of Twins – Monozygotic (MZ) – Dizygotic (DZ) • Four Sources of Information – MZ Twins reared Together – DZ Twins reared Together – MZ Twins reared Apart – DZ Twins reared Apart (Latter two are almost non-existent today)
Monozygotic Twins • Look identical • From same egg • Share 100% of their genes. • Natural clones • Reared together they share some environment • Same age
Dizygotic Twins • Share 50% of their genes on average • Don’t necessarily look exactly the same • Reared together they share some environment • Same age (otherwise just like other siblings)
Analytical Approaches • Correlations (pre-1970) but good heuristic • Correlate the scores of co-twins across families separately for MZs and DZs. (rMZ and rDZ) • What to look for: – if rMZ > rDZ (MZ twins are more similar to each other): Trait is probably heritable – if rMZ = rDZ: Trait is probably environmental – If rMZ > 2*rDz: Dominance (never seen for social traits) • Anova/Ancova/Manova/Mancova (1970‐1977) – Maybe s'll used with very small samples • Structural Equa'on Models with ML (up to date)
Expecta'ons (More Formally) A (Additive Genetic Influence): 2(rMZ – rDZ) (Assumes no Dominance, Gene-Gene or Gene- Environment Interactions) C (Common Environment): 2rDZ – rMZ D (Domiannce): 2rMZ – 4rDZ E (Unique Environment): 1 – MZ ( This also includes all sources of deviation from perfect correlation… like measurement error)
Other Things to Watch Out For • Who is an MZ and who is a DZ – Self report is 95% accurate. (Is that good enough?) • Mixture Model Correc'on (lets not get too far ahead) – Mul' Ques'on Latent Class Analysis – Genotyping • No influen'al outliers • No differences in means and variances between MZ and DZ twins (and between twin 1 and twin2) – For categorical data, same is true for category thresholds • Equal Environemnt Assump'on (more on this later) • No alterna've sources of variance – Self selec'on into certain environments – Random ma'ng of parents
The Univariate Structural Equa'on Model
What else can you do with this model • Explain varinace of “phenotype” with predictors Before Decomposing Residual Variance Into A, C & E – Age and sex is standard. Can use others. • Sex difference (include DZOS) 4, 5, 6 group model • Add Addi'onal Family Members into the Model • Use a measurement (CFA or IRT) model to construct phenotype • Test rela'onships between phenotypes. Decompose the covariance into A, C and E
Biological Pathway: Genomics Behavioral implica'ons can be assessed at each of these steps Proteins: Brain DNA (Genes code for these) Genes Nucleo'des Neurons Amino Acids
What am I doing? (Survey Research) • Na'onal Survey of Midlife Development in the United States (MIDUS) – Wave I was collected in 1995‐1996 – Wave II collected 10 years later (but lot of missing) – Only used items present on both waves – Large Na'onal Representa've Sample – RDD CATI + Mail Follow Up – Oversample of twins (and sibs and urban) – Singleton sample n=3091 – Twins sample nMZ=359 / nDZ=337 pairs
What is Survey Response Style? Acquiescence and Extreme Response
Cholesky longitudinal model (for twin 1)
Panel Cholesky ACE Model Results Variance and Covariance Decomposed into ACE Acquiescence Total A C E ----------------------------------------------- Variance 1 0.286** 0.114 0.600*** Covariance 0.569*** 0.286** 0.114 0.169*** ----------------------------------------------- Extreme Resp. Total A C E ----------------------------------------------- Variance 1 0.196 0.321* 0.483*** Covariance 0.781*** 0.196 0.302+ 0.283*** ----------------------------------------------- +: p<.10, *: p<.05, **: p<.01, ***: p<.001
Personality (Big 5) • Work with Ma=hew Hibbing • Personality (Big 5) – Extraversion – Openness – Agreeableness – Conscien'ousness – Neuro'cism Personality A C E ----------------------------------------------- Agreeableness 0.344*** 0 0.656*** Conscientiousness 0.641*** 0.015 0.344*** Extraversion 0.533*** 0 0.467*** Neuroticism 0.549*** 0.03 0.421*** Openness 0.532** 0.022 0.446*** ----------------------------------------------- **: p<.01, ***: p<.001
Expecta'ons (also on next slide) Personality Acquiescence ------------------------------------------- Agreeableness ++ Conscientiousness ?? Extraversion -- Neuroticism + Openness -- ------------------------------------------- - or + : Weak expectations, -- or ++: Strong expectations • Just Focused on Acquiescence – Personality does not have a C component – Extreme response does not have a significant A
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