The assessment of individual differences between young children with a pervasive developmental disorder by means of behaviour scales which are derived from direct observation.

Data obtained by direct observation of 112 3-6-year-old normal children and 31 children with a pervasive developmental disorder aged 3-6 were used to construct behaviour scales by means of simultaneous component analysis. This is a technique for finding behaviour clusters (components) common to different groups by weighting the variables such that the resulting components maximize variance accounted for when summed over the groups (Milsap & Meredith, 1988, Psychometrika, 53, 123-134; Berge & Kiers, 1990, Nederlands Tijdschrift voor de Psychologie, 45, 221-226). An evaluation of the component structure that was found is given for both groups.

Appropriate conditions for maintenance of chimpanzees in studies with blood-borne viruses: an epidemiologic and psychosocial perspective.

Based on the know epidemiology of the viruses that account for the bulk of the need for chimpanzees in biomedical research--hepatitis B virus (HBV), non-A, non-B (NANB) hepatitis virus, and human immunodeficiency virus (HIV)--as well as the psychosocial needs of this species, requirements for appropriate isolation conditions for these animals have been reviewed. We believe that animals should generally be housed in groups of at least two in the same cage, and that cages encased in solid-walled isolator boxes for housing of single chimpanzees are unnecessary for virologically adequate isolation for studies of HBV, NANB and HIV, and cause sensory and psychosocial deprivation, which contravenes their psychological well-being.

Detection of low dose effects of psychopharmaca: Application of a semi-Marcov model to rhesus monkey behaviour.

Behavioural testing of psycho-active drugs at lower doses is needed for medical applications and for the study of pharmacological brain mechanisms. Sensitive methods to detect effects on the time structure of behaviour are lacking. We propose a procedure based on a description within the framework of continuous time Marcov chain models.

Regulation of nursing in chimpanzees.

The regulation of nursing was studied in captive chimpanzees from birth to 6 months of age. It was asked whether regulation was predictable or timing was irregular. A search for unimodal frequency distributions resulted in a distinction among nursing bouts, nursing episodes (bouts with brief interruptions) and nursing pauses.

Quantitative criteria for attention and activity in child psychiatric patients.

The aim was to find empirically justified criteria for attention and activity. Patients with various disorders and controls were observed during psychiatric examinations. Measures of attention increased with age, were lower in patients than controls, were correlated with each other and related to the quality of task performance.