374 game with three other children (who were also under treatment in the clinic but did not participate in the study). The setting was organized using a video script to both standardize the behaviour samples and elicit a range of naturalistic child behaviours. The video script was tested in a previous study [16]. A 17-min videotaped behaviour sample was obtained for each of the target children. Each mother and each group-care worker observed only one target child on videotape (along with the three other chil- dren who volunteered in playing with the target child). To attain a behaviour sample for a control child, two additional 17-min recordings were made within the same setting for two children, one of each sex. Each observer also viewed a videotape of a male or female ‘unknown’ (control) child, depending on the sex of the ‘known’ child (to control for the inﬂuence of sex of the child on variations between familiar and unfamiliar child ratings). These two control children were carefully selected to make sure that none of the professionals (or mothers) participating in the study were familiar with them. The videotapes of the two control children were recorded in the same clinic using the same standardized setting as was used for the known children. The mothers and group-care workers were asked to watch the videotapes of a (well) known child and an unknown child individually and then assess the behaviour problems observed on the videotapes. The order of pre- sentation for the videotapes of the known and unknown children was counterbalanced. The sex of the unknown child was matched to the sex of the known child, to control for a possible contaminating effect of sex differences on the child behaviour ratings. The sessions were all con- ducted at the clinic by trained research assistants (N = 5) who were unfamiliar with the target children. The research assistant conducting the session with a particular informant was also unaware of the ratings provided by the other informants for the same child. The mothers and group-care workers were asked to assess the behaviour problems observed on the videotape using the DOF immediately following the viewing of each videotape. The independent criterion observations for the 55 target children and two control children were performed indi- vidually by two undergraduate psychology students with previous training on child observation and assessment. The independent observers were given additional training on the DOF by an experienced observer until an inter-rater Kappa for the DOF items of at least 0.80 on a set of ﬁve pilot videotapes was reached. The ﬁnal inter-rater agree- ment between the independent observers on the videotapes of the target children was found to be 0.85 (n = 55). After their initial—individual—rating of the target videotapes, the independent observers further discussed any discrep- ancies until consensus was reached. The independent 123 Eur Child Adolesc Psychiatry (2010) 19:371–377 observers were instructed to review the videotapes as many times as they felt necessary, and the agreed-upon scores were used in all of the statistical analyses. The mothers, group-care workers and independent observers were all instructed to rate only those behaviours which they had actually observed on the videotape. Data analyses The effects of acquaintanceship were evaluated in a repe- ated-measures ANOVA for the DOF video ratings with informants (i.e., mothers, group-care workers, independent observers) as the within-subjects factor. Planned contrasts were tested for the differences between (1) mothers versus independent observers, (2) group-care workers versus independent observers and (3) mothers versus group-care workers. Separate analyses were conducted on the DOF ratings of the known and unknown children. For the known children, the analyses involved those video recordings which were rated by all three types of informants. This meant the rat- ings provided by 44 mothers, 26 group-care workers who rated the same 44 videos (with some group-care workers rating more than one video), and the ratings of the same 44 videos by the independent observers averaged across the two observers per video. For the unknown (or control) children, the mothers and group-care workers were all asked to rate the videotape of the male or female control child depending on the sex of the known child being rated by them. Given that each of the group-care workers rated the videotape of only one control child, the sample size was thus reduced to 26 videos for the analysis of the unfamiliar child ratings. The independent observers rated the video- tapes of both the male control child and the female control child. For the analyses of the ratings of the unknown children, each rating of an unknown control child by the mother was matched with the rating control child of the same sex by the independent observers and a possibly differential effect of sex of the unknown child was thus avoided in such a manner. Results Descriptive data The means and standards deviations for the child behaviour ratings (DOF) provided by the mothers, group-care workers and independent observers are presented in Table 1. In order to attain an indication of the level of problem behaviour occurring on the videos, the DOF behaviour problem scores produced by the informants were compared to the DOF scores presented in the Manual for the ASEBA