Eur Child Adolesc Psychiatry (2010) 19:371–377 Table 1 Raw scores and ANOVA results for known and unknown child behaviour ratings by different informants Informant Known child ratings (DOF) Mothers Group-care workersa Independent observers Unknown child ratings (DOF) Mother Group-care workers Independent observersb N 44 44 44 26 26 26 M 25.95 35.70 12.23 18.27 34.62 17.88 SD Repeated measures (GLM) Planned contrast 13.95 20.06 5.78 16.02 20.34 3.17 Mothers versus independent observers Group-care workers versus independent observers Mothers versus independent observers Group-care workers versus independent observers df 1.43 1.43 1.25 1.25 F 47.62 68.95 0.02 19.01 375 p 0.000 0.000 0.902 0.000 a Multiple observations per group-care worker b The numbers of ratings of male versus female control children by the independent observers was matched with the number of male versus female control children rated by the mothers School-age Forms and Proﬁles [3]. In the Manual, an average total problems score of 9.1 (SD = 4.1) is reported for trained observers rating 10-min samples of classroom behaviour for referred children. In our study, the inde- pendent observers assigned an average total problems score of 12.23 to the videotaped behaviour samples for the children well known to the mothers and group-care workers and an average score of 17.88 to the videotaped behaviour samples for the two unknown control children. Taking the difference in the durations of the videotapes into consid- eration (i.e., 10 min for the normative sample vs. 17 min for the present sample), we can conclude that the inde- pendent observers viewed roughly the same level of problem behaviours in the present sample as the trained observers in the normative sample of referred children. Acquaintanceship The results of the repeated-measures ANOVA to evaluate the inﬂuence of acquaintanceship on the ratings of child behaviour problems are also presented in Table 1. The multivariate statistics show signiﬁcant overall group dif- ferences for the known child ratings (F(1,41) = 93,81, p = 0.000) as well as for the unknown control children (F(1,23) = 254,45, p = 0.000). The planned contrasts further show the mothers to report signiﬁcantly higher levels of problem behaviour than the independent observ- ers in the case of known children but not in the case of unknown children. The acquaintanceship hypothesis is thus conﬁrmed by the mothers in our study. The group-care workers, however, reported signiﬁcantly higher levels of problem behaviour for both the known and unknown children than the independent observers, which suggests that the acquaintanceship hypothesis is only partially con- ﬁrmed by the ﬁndings for the group-care workers. Discussion Drawing on theories of personality judgment, a research design was adopted to examine the role of acquaintance- ship on perceptions of child behaviour. On the basis of the acquaintanceship hypothesis, we expected both mothers and group-care workers to report signiﬁcantly higher levels of problem behaviours for known children than indepen- dent observers but similar levels of problem behaviours for unknown children. Mothers rating their own children’s behaviour were indeed found to perceive more behaviour problems than independent observers. In fact, the mothers in our study reported twice as many problem behaviours for their own children as the independent observers, which is in line with the ﬁndings of earlier research [20, 21]. We also found mothers to perceive similar levels of problem behaviours for unknown children when compared to independent observers for the same children. Taken toge- ther, these results indicate an acquaintanceship effect. However, the acquaintanceship hypothesis is only partially conﬁrmed by the ﬁndings for the group-care workers. While these professionals reported more behaviour prob- lems for the known children than the independent observ- ers did, the group-care workers did not report different levels of problem behaviour for the known versus unknown children. The differential pattern of observation reported for the mothers versus independent observers for the behaviour of known versus unknown children suggests that mothers are indeed more accurate observers of their own children’s behaviour than independent observers. Further evidence suggesting that mothers are generally quite accurate observers of their own child’s behaviour and not biased in their reporting with regard to such is provided by the fact that the group-care workers in our study also reported 123