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\nathan\RaterBias Observer Ratings: Dealing with rater bias Nathan Gillespie Meike Bartels John Hewitt Multiple raters Rather than measure individual’s phenotypes directly, we often rely on observer ratings Example Parent & teacher ratings of children Problem How do you handle bias which is a tendency of a rater to over or underestimate scores consistently Response Bias - stereotyping, different normative standards, response style Projection Bias - psychopathology of the parent influences his/her judgement of the behavior of the child e.g. several studies suggest that depression in mothers may lead to overestimating their children’s symptoms Rater bias can inflate C How to disentangle child’s phenotype from rater bias? Example of multiple rater data: Problem behavior Data from Netherlands Twin Registry Questionnaires ages 3, 5, 7, 10 & 12 - maternal & paternal ratings ages 7, 10, and 12 - teacher ratings ages 12, 14, 16 - self report Internalizing - Anxious/Depressed, Somatic Complaints & Withdrawn subscales Externalizing - Aggressive & Rule Breaking subscales. Mother's & father's ratings of aggressive behaviour in boys at 12 yrs Multiple raters Analysis of parent / teacher ratings depends on assumptions YOU make! 1. Biometric model – agnostic i.e. treat data as assessing different phenotypes. Good if mothers and fathers rate / observe kids in different situations! 2. Psychometric model – assume there is a common phenotype assessed by both parents + specific effects uniquely observed by each each parent 3. Rater bias model – Ratings of a child’s phenotype modeled as a function of child’s phenotype + bias introduced by the rater 1. Biometric model Model mother's and father's ratings agnostically The mother's and father's ratings may be correlated but for unspecified reasons. Mothers' and fathers' ratings are assessing different phenotypes. - ratings are taken across different situations - mums and dad don't have a common understanding of the behavioural description In this case we would simply model the ratings in terms of a standard bivariate analysis 1. Biometric model Treat parental ratings as separate phenotypes A C δc11 δc21 δe11 δa21 δa11 A E C δe21 δa22 δc22 δc11 δe21 Mother's ratings E Father's ratings δe22 The Mx script Script Cholesky1.mx Data: TAD.dat Task Fix error & calculate standardized variance components Variance-covariance matrices in Mx MZ (A+C+E | A+C_ A+C | A+C+E ) ; DZ (A+C+E | [email protected]+C_ [email protected]+C | A+C+E ) ; Polychoric correlations 1. 2. 3. 1. Mother T1 1.00 2. Father T1 .72 1.00 3. Mother T2 .71 .57 1.00 4. Father T2 .57 .71 .73 4. 1.00 Variance Decomposition A C E Mother's ratings .59 .23 .18 Father's ratings .58 -2LL .28 .14 3243.16 df 1816 2. Psychometric Model More restrictive assumptions There is a common phenotype which is being assessed by mothers and fathers AND There is a component of the each parent's ratings which assesses an independent aspect of the children's behaviour. Mother and father ratings would therefore correlate because they are making assessments based on shared observations and shared understanding of the behavioural descriptions 2. Psychometric Model 1 1,½ A C E c e A a em cm am Em e Reliable trait variance T2 Father’s rating T2 Father’s rating T1 ef c a Reliable trait variance T1 Mum’s rating T1 E C cf Cm af af Am Am cf Cm Mum’s rating T2 ef Em am cm em 1,½ Em Cm Am Am 1 1,½ 1 Cm Em Total variance for an individual MRT1 1 = FRT1 1 am 0 Am af cm 0 + x 0 a A + c C + e E x Af Cm 0 cf em 0 + x Cf + Em x 0 ef Ef The Mx script Script Psychometric1.mx Data TAD.dat Task Fix error & note variance components Variance-covariance matrices in Mx MZ DZ (G+S+F | G+S_ G+S | G+S+F) + (G+S+F | [email protected]+S_ [email protected]+S | G+S+F) + L * (A+C+E | A+C_ A+C | A+C+E ) * L' ; L * (A+C+E | [email protected]+C_ [email protected]+C | A+C+E ) * L' ; Variance decomposition Mother's ratings Father's ratings Latent factor A .42 .39 C .14 .13 E .03 .03 Residuals Ares .17 .19 Cres .09 .14 -2LL df Eres .14 .11 3243.16 1816 Rater Bias Model Even more restrictive Assumes that there is a common phenotype which is being assessed by mothers and fathers Phenotype is again a function of three latent factors underlying the ratings of both mothers and fathers: a genetic factor (A), a shared environmental factor (C), and a non-shared environmental factor (E). Rater-specific factors are modeled: a maternal rater bias factor, a paternal rater bias factor, & residual (unreliability) factors affecting each rating. The influence of the common factors is assumed to be independent of the maternal and paternal rater bias and unreliability factors. Rater Bias Model 1 1,½ A C E e c A a c a Reliable trait variance T1 1 e Reliable trait variance T2 1 1 mother rating T1 father rating T1 rm rf Rm T1 E C 1 mother rating T2 father rating T2 rm Rf T1 rf Rm T2 Rf T1 bf bm bm Mum’s bias bf Dad’s bias Total variance for an individual MRT1 1 = a A + c C + e E x FRT1 1 bm 0 Bm + x 0 bf Bf Rm rm 0 x 0 rf Rf + The Mx script Script Raterbias1.mx Data TAD.dat Task Fix error & note variance components Variance-covariance matrices in Mx MZ DZ (S+F | S_ S | S+F) + (S+F | S_ S | S+F) + L * (A+C+E | A+C_ A+C | A+C+E ) * L' ; L * (A+C+E | [email protected]+C_ [email protected]+C | A+C+E ) * L' ; Variance decomposition Mother's ratings Father's ratings Latent factor A .53 .51 C .05 .05 E .00 .00 Residuals Rater Bias .23 .29 -2LL df Eres .19 .15 3257.37 1818 Results: Model comparison -2LL df BIC Cholesky 3243.16 1816 -1171.22 Psychometric 3243.16 1816 -1171.22 Rater Bias 3257.37 1818 -1167.19 Conclusions 1. Rater bias, if not controlled for, ends up in shared environment 2. Besides rater bias, rater specific views are a source of rater disagreement > multiple rater design valuable 3. Psychometric model provides most information on sources of rater disagreement Sibling Interaction / Rater Contrast 1 1 vs 0.5 e A C E c A a E C a c e s Twin 2 Twin I s Path s implies an interaction between phenotypes Workshop on Multivariate Modelling of Genetic Data Egmond 2005 Sibling Interaction Social Interaction between siblings (Carey, 1986; Eaves, 1976) Behaviour of one child has a certain effect on the behavior of his or her co-twin: Cooperation - behavior in one twin leads to like-wise behavior in the cotwin Competition - increased behavior in one twin leads to decreased behavior in co-twin Workshop on Multivariate Modelling of Genetic Data Egmond 2005 Rater Contrast Behavioural judgment / rating of one child of a twin pair is NOT independent of the rating of the other child of the twin pair. Rate compares the twins behaviour against one another The behaviour of the one child becomes a ‘standard’ by the which the behaviour of the other co-twin is judged / rated. Parents may either stress the similarities or differences between the children Effects of rater contrast Phenotypic cooperation / positive rater contrast Mimics the effects of shared environment Increases the variance of more closely related individuals (var MZ >> var DZ) Phenotypic competition / negative rater contrast Mimics the effects of non-additive genetic variance Increases the variance of more closely related individuals the least (var MZ << var DZ) Numerical Illustration a2=0.5, d2=0, c2=0, e5=0.5 S = 0; cooperation >> s = 0.5; competition >> s = -0.5 MZ DZ Unrelated Var Cov r Var Cov r Var Cov r 1 .50 .50 1 .25 .25 1 0 0 Cooperation 3.11 2.89 .93 2.67 2.33 .88 2.22 1.78 .80 Competition 1.33 .44 .33 1.78 -.67 -.38 2.22 -1.78 -.80 None Social interactions cause the variance of the phenotype to depend on the degree of relationship of the social actors Contrast Effect 1 1 vs 0.5 e A C E c A a E C a c e s Twin 2 Twin I s P1 = sP2 + aA1 + cC1 + eE1 P2 = sP1 + aA2 + cC2 + eE Contrast Effect P1 0 s P1 = P2 + s 0 P2 A1 C1 a c e 0 0 0 E1 A2 0 0 0 a c e P1 = sP2 + aA1 + cC1 + eE1 P2 = sP1 + aA2 + cC2 + eE2 C2 E2 Matrix expression y = By + Gx y – By = Gx (I-B) y = Gx (I-B)-1 (I-B)y = (I-B)-1 Gx y = (I-B)-1 Gx Mx Begin Matrices; B full 2 2 End Matrices; Begin Algebra; P = (I-B)~; End Algebra ! constrast effect Variance – Covariance Matrix MZs P & ( A + C + E | A + C_ A + C | A + C + E) / DZs P & ( A + C + E | [email protected] + C_ [email protected] + C | A + C + E) / The Mx script Script: Contrast.mx Data: TAD.dat Consequences for variation & covariation Basic model X1 X2 x x P1 P1 = sP2 + xX1 s s P2 P2 = sP1 + xX2 In matrices X1 X2 x x s P1 P1 P2 P2 s 0 s = s 0 P1 x 0 X1 0 x X2 + P2 y = By + Gx Matrix expression y = By + Gx y – By = Gx (I-B) y = Gx (I-B)-1 (I-B)y = (I-B)-1 Gx y = (I-B)-1 Gx Matrix expression y = (I-B)-1 Gx where (I-B) is 1 0 0 s 0 1 1 -s = s 0 -s 1 Which has determinant: (1*1-s*s) = 1-s2 , so (I-B)-1 is 1 1-s2 1 s @ s 1 Matrix expression Variance-covariance matrix for P1 and P2 Σ { yy’} = { (I-B)-1 Gx} { (I-B)-1 Gx}’ = (I-B)-1 G Σ {xx’} G’ (I-B)-1’ where Σ {xx’} is covariance matrix of the x variables Matrix expression X1 X2 x x P1 s P2 s We want to standardize variables X1 and X2 to have unit variance and correlation r, therefore Σ {xx’} = 1 r r 1 To compute the covariance matrix recall that… x 0 G= 0 x 1 (I-B)-1 = 1-s2 1 r Σ {xx’} = r 1 1 s @ s 1 To compute the covariance matrix recall that… Σ { yy’} = x2 (1-s2)2 1 + 2sr + s2 r+2s + rs2 @ r+2s + rs2 1 + 2sr + s2 The effects of sibling interaction on variance and covariance components between pairs of relatives Source Additive genetic Dominance Shared env Non-shared env Variance ω(1+2sra+s2)a2 ω(1+2srd+s2)d2 ω(1+2src+s2)c2 ω(1+2sre+s2)e2 where ω = scalar 1/(1-s2)2 Covariance ω(ra+2s+ras2)a2 ω(rd+2s+rds2)d2 ω(rc+2s+rcs2)c2 ω(re+2s+res2)e2 Rater Bias Influence shared environmental variance! Independent of zygosity Response Bias - stereotyping, different normative standards, response style Projection Bias - Psychopathology of the parent influences his/her judgement of the behavior of the child e.g. several studies suggest that depression in mothers may lead to overestimating their children’s symptomology Multiple raters Rather than measure individual’s phenotypes directly, we rely on observer ratings. Example: Parent & teacher ratings of children’s behaviour Problem: How to disentangle child’s phenotype from rater bias? Rater bias can influence C (independent of zygosity) Parental Disagreement Rater bias / error (e.g. response style, different normative standards) Mother or father provide specific information - distinct situations, parent-specific relation with child Rater Bias Parental ratings Agreements versus Disagreements