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#

2 Models for Multiple Rating Data

A primary source of information about a child's behavior is the
description of that behavior by his or her parents. In the study of
child and adolescent psychopathology for example, parental reports are
fundamental to the widely used assessment system developed by
Achenbach and Edelbrock (1981). However, different informants do not
generally agree in detail about a given child's behavior (Achenbach
*et al.*, 1987; Loeber *et al.,* 1989) and, of course, there
are very good reasons why this should be so (Cox and Rutter, 1985).
Different informants, such as the child, parents, teachers or peers,
have different situational exposure, different degrees of insight, and
different perceptions, evaluations and normative standards that may
create rater differences of various kinds in reporting problem
behaviors. How we analyze parental ratings of children's behavior,
and the models we employ in the course of our analyses, will depend on
the assumptions we make. In this chapter we discuss the application
of three classes of models -- biometric, psychometric, and bias
models.
First, suppose we took an agnostic view of the relationship between
the ratings by different informants by thinking of them as assessing
different phenotypes of the child. The phenotypes may be correlated
but for unspecified reasons. This view may be appropriate if mothers
and fathers reported on behaviors observed in distinct situations, or
if they did not share a common understanding of the behavioral
descriptions. In such a case it would be appropriate to treat the
analysis of mothers' and fathers' ratings as a standard bivariate
genetic and environmental analysis where the two variables are the
mothers' ratings and fathers' ratings. We shall refer to the class of
standard bivariate factor model as *biometric models* (see
Chapter 10 for examples).
Second, suppose we made the more restrictive assumption that there is
(i) a common phenotype of the children which is assessed both by
mothers and by fathers, and (ii) a component of each parent's ratings
which results from an assessment of an independent aspect of the
child. Mothers' ratings and fathers' ratings would correlate because
they are indeed making assessments based on shared observations and
have a shared understanding of the behavioral descriptions used in the
assessments. In this case, we approach the analysis of parental
ratings through a special form of model for bivariate data which we
will refer to as *psychometric models* (see Chapter 10
for examples).
Third, we consider a model of *rater bias.*
Bias in this context is considered to be the tendency of an individual
rater to overestimate or underestimate scores consistently. This
tendency is a deviation from the mean of all possible raters in the
rater group; no reference is made here to any external criterion such
as a clinician's judgement. Neale and
Stevenson (1989) considered the general problem of rater bias and the
particular issues of parental biases in ratings of children. They
presented a model in which the rating of a child's phenotype is
considered to be a function both of the child's phenotype and of the
bias introduced by the rater. In this way it is possible, when two
parents rate each of their twin children, to conduct a behavior
genetic analysis of the variation in the latent phenotype while
allowing for variation due to rating biases. If the rater bias model
adopted by Neale and Stevenson (1989) provides
an adequate account of the ratings of children by their parents, it
becomes possible to partition the variance in these parental ratings
into their components due to reliable trait variance, due to parental
bias , and due to unreliability or error in
the particular rating of a particular child. The reliable trait
variance can then be decomposed into its components due to genetic
influences, shared environments, and individual environments. Since
rater bias models represent restricted special cases for the parental
ratings of more general biometric and psychometric models of the kind
discussed by Heath *et al.*, (1989) and
McArdle and Goldsmith (1990) and in
Chapter 10 of this volume, it is possible to compare the
adequacy of bias models with the alternative bivariate psychometric
and biometric models. Further, comparison of the biometric and
psychometric models indicates how reasonable it is to assume that two
raters are assessing the same phenotype in a child. As we move from
the biometric to the psychometric to the bias models, our assumptions
become more restrictive but, if appropriate, our analyses become more
directly informative psychologically. Here we outline how an analysis
of parental ratings using the bias model can be implemented simply
using Mx. We discuss the properties of the alternative models and
illustrate their application with data from a twin study of child and
adolescent behavior problems.

**Subsections**

** Next:** 1 Rater Bias Model
** Up:** 11 Observer Ratings
** Previous:** 1 Introduction
** Index**
Jeff Lessem
2002-03-21