Journal of Personality and Social Psychology1989. Vol. 56, No. 3, 446-455Copyright 1989 by the American Psychological Association, Inc.0022-3514/89/S00.75Rater Bias in the EASI Temperament Scales: A Twin StudyM. C. NealeDepartment of Human GeneticsMedical College of VirginiaJ. StevensonUniversity of SurreyGuildford, Surrey, EnglandUnder trait theory, ratings may be modeled as a function of the temperament of the child and thebias of the rater. Two linear structural equation models are described, one for mutual self- and part-ner ratings, and one for multiple ratings of related individuals. Application of the first model to EASItemperament data collected from spouses rating each other shows moderate agreement betweenraters and little rating bias. Spouse pairs agree moderately when rating their twin children, but thereis significant rater bias, with greater bias for monozygotic than for dizygotic twins. MLE's of herita-bility are approximately .5 for all temperament scales with no common environmental variance.Results are discussed with reference to trait validity, the person-situation debate, halo effects, andstereotyping. Questionnaire development using ratings on family members permits increased rateragreement and reduced rater bias.In trying to establish the origins of individual differences intemperament and personality, the family provides an importantand unique source of information. Within this setting, familymembers are able to observe one another's behavior across ex-tended time periods and a wide variety of situations. However,there are a number of issues concerning the accuracy of mea-surement in such a setting that must be considered before sub-stantive conclusions can be drawn about the influences on indi-vidual differences.A major difference between personality measurement inadults and in young children is that adult personality measure-ment is usually based on a self-report questionnaire, and juve-nile personality is typically assessed by another rater, often aparent. Each of these methods of personality assessment hasmeasurement difficulties; some of these problems are commonto both forms of measurement, and others are specific to oneor the other. In family studies of personality, the associationsbetween these two types of measure are obtained and com-pared. The use of twins or adoptees allows the estimation ofgenetic and environmental influences on individual differences.Before such data can be interpreted, the limitations posed bythe measurement techniques need to be established. The aimof this paper is to demonstrate how data from families contain-ing twin children can be used to quantify some of the influenceson personality measures and consequently can provide moresensitive and complete estimates of the influences on individualdifferences in personality.The accuracy of measures of personality has recently beenreviewed by Funder (1987). He has argued for the need to estab-lish a systematic account of social judgments in everyday situa-tions outside the laboratory. In this context, the emphasisshould be on whether judges agree with one another rather thanon sources of error in social judgments, as is more often the caseCorrespondence concerning this article should be addressed to M. C.Neale, Department of Human Genetics, Medical College of Virginia,Box 33, Richmond, Virginia 23298.in social psychological investigation. Funder went on to suggestthat as long as subjects are well known to each other, one canobtain at least modest degrees of agreement between self-reportand ratings by another. The prevailing theoretical accounts ofpersonality have tended to make strong arguments for the sa-lience of situational factors (e.g., Bern & Allen, 1974; Mischel,1968),traits(e.g.,Cattell, 1982;Eysenck, 1967;McCrae, 1982),or situation-trait interactions (e.g., Epstein, 1983). It is clearthat any satisfactory theory will have to take into account eachof these sources of influence on an individual's behavior in anyone setting (Pervin, 1985). The case for predictive validity oftraits is particularly strong when measurements are aggregated(Rushton, Brainerd, & Pressley, 1983), or when some measureof consistency of the trait within the individual is incorporated(Kenrick & Stringfield, 1980). The contrast between the situa-tionist and trait positions has been highlighted recently in thedebate about the nature of temperament differences in children(Goldsmith et al., 1987). Rowe (1987) has argued that researchdesigns that allow a separation of genetic and environmentalinfluences can help to resolve some of the issues in the person-situation debate. However, before family or twin data, or both,can be used to resolve the issues surrounding situational andperson-centered influences on behavior, important measure-ment issues need to be addressed.There are numerous general problems with the use of self-report and rating scales, including response biases, ambiguousitems, faking, and acquiescence. Generally, these problems leadto reduced correlation with external validating measures, pro-vided that the external measures are not subject to the samesources of systematic bias. These difficulties have been stressedby Nisbett and Wilson (1977); nevertheless, a case for self-re-port data has been made by Averill (1983). With subtle ques-tionnaire design and low motivation of volunteer samples topresent a favorable image, these difficulties can be minimized(Cronbach, 1970). Self-ratings of personality are potentiallysubject to a variety of sources of inaccuracy associated withintrospection. When responding to questionnaire items, thesubject relies on his or her self-concept, which may be inaccu-446RATER BIAS IN TEMPERAMENT447rate for a number of reasons. One popular school of thought,known as symbolic interactionism (Schrauger & Schoeneman,1979) has suggested that the idea of the self is built up as a re-flection of the way one appears to others. If the behavior of oth-ers toward the self were not consistent, an essentially randomself-concept would emerge, which would fail to correlate withother ratings or behavioral or physiological variables. Even ifthe behavior of others toward the self were consistent, the look-ing-glass self-image could be inaccurate for several reasons.First, the sample of individuals from whom feedback informa-tion is obtained might not be a representative sample of thepopulation. Second, the perception of the attitudes and re-sponses of others may itself be inaccurate.