AGGRESSIVE BEHAVIOR Volume 36, pages 351–357 (2010) Identifying Early Signs of Aggression: Psychometric Properties of the Cardiff Infant Contentiousness Scale Dale F. Hay 1 , Oliver Perra 1 , Kathryn Hudson 1 , Cerith S. Waters 1 , Lisa Mundy 1 , Rebecca Phillips 1 , Ian Goodyer 2 , Gordon Harold 3 , Anita Thapar 1 , Stephanie van Goozen 1 , and the CCDS Team 1 1 Cardiff University, Cardiff, Wales, United Kingdom 2 University of Cambridge, Cambridge, England, United Kingdom 3 University of Otago, Dunedin, New Zealand : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Our aim was to develop an age-appropriate measure of early manifestations of aggression. We constructed a questionnaire about normative developmental milestones into which a set of items measuring infants’ use of physical force against people and expressed anger were included. These items comprise the Cardiff Infant Contentiousness Scale (CICS). Evidence for the reliability and validity of the CICS is provided from analyses of a sample of N 5 310 British infants, assessed at a mean age of 6 months as part of a larger longitudinal study of the development of aggression. The informants’ CICS ratings demonstrated reasonable levels of internal consistency and interrater agreement. Informants’ ratings were validated by observations of infants’ distress in response to restraint in a car seat. Longitudinal analyses revealed that contentiousness was stable over time and that contentiousness at 6 months predicted infants’ later use of force with peers. When used in the company of other methods, the simple four-item CICS scale could serve as a useful screen for early manifestations of aggressiveness in human infants. Aggr. Behav. 36:351–357, 2010. r 2010 Wiley-Liss, Inc. : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : Keywords: aggression; anger; contentiousness; infants INTRODUCTION In recent years, there has been an increasing aware- ness that serious aggressiveness, oppositionality, and conduct problems are already apparent in early childhood [Egger and Angold, 2006; Keenan and Wakschlag, 2004; Keenan et al., 1998; Kim-Cohen et al., 2005; Wakschlag et al., 2007]. It has long been recognized that the early onset of conduct problems identifies a subgroup of youngsters with neurobio- logical deficits and lifelong persistence in antisocial behaviour [e.g., Raine et al., 2005]. This fact has stimulated interest in the possibility of applying clinical diagnostic criteria to 2- and 3-year-olds [e.g., Egger et al., 2006], and in identifying even earlier manifestations of aggressiveness and externa- lizing problems in 1- and 2-year-olds [e.g., Coˆ te´ et al., 2006; Dionne et al., 2003; Tremblay et al., 2004; van Zeijl et al., 2006]. Infants’ use of physical force against other people can be seen as early as 12 months of age, as indicated by informants’ reports [Alink et al., 2006] and observations of early interaction between peers: 12-month-olds engage in physical force at the same rate as 24-month-olds [Caplan et al., 1991]. Developmental trajectory analyses have shown that toddlers who engage in physical force at high rates show a pattern of increasingly frequent and intense aggressiveness over childhood [e.g., Coˆ te´ et al., 2006; NICHD Early Child Care Research Network, 2004; Tremblay et al., 2004]. These studies, in turn, raise the possibility that early manifestations of aggression might be identi- fied even earlier, in the first year of life, when infants are first developing the motor ability to direct force against other people. Our aim in this article is to describe the psychometric properties of a brief scale that measures younger infants’ propensities to engage in conflict with their companions; children’s capacity for aggression develops in the social context Published online 4 October 2010 in Wiley Online Library (wiley onlinelibrary.com). DOI: 10.1002/ab.20363 Received 9 June 2009; Accepted 7 July 2010 Grant sponsor: Medical Research Council Programme Grant; Grant number: GO400086. Correspondence to: Dale F. Hay, Cardiff University, Wales, UK. E-mail: haydf@cardiff.ac.uk r 2010 Wiley-Liss, Inc.