Eur Child Adolesc Psychiatry (2010) 19:371–377 mothers and group-care workers who were well acquainted with these children versus independent observers not acquainted with these children will be evaluated. In order to provide convincing evidence for an effect of acquain- tance, two different conditions are employed. First, moth- ers and group-care workers are asked to rate the amount of problem behaviour for video recordings of both known and unknown children. Second, independent observers who did not previously know the children, thus, are also asked to rate the same videos. This design allows us to compare (a) the ratings of known versus unknown children by the same judges and (b) the ratings of judges who were acquainted with versus strangers to the same children. In keeping with the hypothesis of an acquaintanceship effect, we expected the mothers and group-care workers to consistently report higher levels of problem behaviour for the known children when compared to the independent observers but similar levels of problem behaviour for the unknown children when compared to the independent observers. Method Participants The participants were 55 mothers of 43 boys and 12 girls aged 6–13 years (M = 8.9, SD = 1.9) in residential or day- treatment programs at Entre´a, a Dutch clinic for the treat- ment of youth with emotional and behavioural problems. The mean age of the mothers was 38.5 years (SD = 4.8, range of 25–52 years). All of the children were diagnosed with psychiatric disorders such as Attention deﬁcit hyper- activity disorder, pervasive developmental disorder, oppo- sitional deﬁant disorder or conduct disorder according to the DSM-IV [4]. None of the children met the criteria for mental retardation. The occupational status of the mothers was categorized using the social demographic inventory (SDI) [19]. Along a six-point scale ranging from (1) unskilled labour to (6) academic career, the median SDI score was 3. The mothers signed consent forms and were given a gift with a value of 15 euros after their participation. The group-care workers for the same children were similarly invited to participate in the present study. To insure consistency of acquaintance with the children, those workers who had known the target child for less than 6 months were excluded from the study. Other group-care workers were not included due to job change, illness or unwillingness to participate. The ﬁnal sample included 26 (or 80%) of the group-care workers who were initially asked to participate. Some of the 26 group-care workers worked with more than one of the children whose mothers participated in the study, which resulted in 44 worker-child 373 dyads. The mean age of the group-care workers was 33.0 years (SD = 6.77); 81% was female. All of the group- care workers had a college degree in special education. The professional experience of the group-care workers ranged from 1 to 20 years (M = 6.8, SD = 5.1). The group-care workers were also given a gift with a value of 15 euros after their participation. The recruitment procedure is described in greater detail in Kroes et al. [14]. Measures Direct observation form (DOF) The DOF [1, 6] was designed to assess the behaviour problems observed in—among other settings—classrooms and group activities. The DOF is easy to use with teacher aids and research assistants after training by an experienced observer [3]. The DOF consists of 96 items, 72 of which have counterparts in the CBCL. Each item is rated along a scale ranging form 0 (=no observed occurrence of the behaviour) to 3 (=deﬁnite occurrence with severe intensity or a duration of three or more minutes). The sum of all the items constitutes the total problems score, which we used in our analyses. The DOF is normally completed after 10 min of live observation. In the present study, which involved the rating of videotapes, an alternative assessment procedure was followed. Rather than complete the DOF form, the infor- mants were asked to sort a deck of 96 cards with the DOF items listed separately on them in two steps directly following the viewing of a videotape. In the ﬁrst step, the mothers, group-care workers or independent observers were asked to select those DOF items which they deﬁnitely did not observe on the videotape. These cards were then removed from the deck and assigned a score of 0 by the interviewers. In the second step, the informants were asked to sort the remainder of the cards into three piles reﬂecting a DOF rating score of 1, 2 or 3 for the item. Written descriptions of the rating scores were present to facilitate the sorting process. The interviewers subsequently trans- ferred the results of the sorting procedure onto the DOF form. This two-step assessment procedure was designed to promote very deliberate decisions regarding each item and consistent application of the scoring procedure across informants. Procedure Videotape recordings were made of the behaviours of the target children, i.e. the children of the mothers who par- ticipated in the study. These recordings were made in a standardized setting in the treatment centre which showed one of the target children interacting in playing a board 123