INTRODUCTION The synonymous terms Autism spectrum disorders and Pervasive developmental disorders refer to a wide continuum of associated cognitive and neuron behavioral disorders, including three core defining features: Impairments in socialization, impairment in verbal and nonverbal communication and restricted and repetitive pattern of behaviors (American Psychiatric Association [APA], 1994). Researchers had also suggested that a pattern of stereotyped and repetitive behavior is a common feature of autism (Bailey et al., 1996). Currently, DSM-IV (APA- 1994) includes five possible diagnoses under the PDD umbrella, include Autistic disorder, Aspergers disorder, PDD-NOS(Pervasive developmental disorder- Not otherwise specified), Childhood disintegrative syndrome, and Rett syndrome, which were concordant with the International Classification of Disease, 10th edition (ICD-10).Epidemiology and prevalence More recent epidemiological studies report an even higher prevalence rate of around 60 per 10,000 (Chakrabarti and Fombonne, 2005) to 116 per 10,000 (1% of the population, Bird et al., 2006). While this substantial increase in the prevalence of ASD probably reflects a better identification of the disorders, due in part to used, areal increase in the incidence of ASD cannot be entirely ruled out. In India a study by Malhotra et al (2003) compared the socio-demographic and clinical profile of PDD patients registered at CAP (Child and Adolescent Psychiatry clinic), PGIMER (Post Graduate Institute of Medical Education and Research) and Chandigrah between 1989 and 1999. Out of 2942 cases 46 cases (1.6%) met ICD-10 criteria for different PDDs.Aetiology of Autism The precise aetiology of Autism remains essentially unknown, despite considerable research into the genetic, biological, pharmacological and environmental factors involved in the development and manifestation of the disorder (Whitely, Rodgers & Shattock, 1998). There is agreement that autism is caused by a dysfunction in the central nervous system with an underlying genetic bases, there are conflicting views as to its defining characteristics and the casual explanation linking brain dysfunction to behavioral characteristics(Kusch & Refermann, 1995). Additionally, it is agreed that Autism can be defined at three different interdependent levels, as a neurological disorder related to brain development, as a psychological disorder affecting cognitive, emotional and behavioral development and lastly as a relationship disorder to develop age appropriate socialization skills. The third aspect of agreement involves the idea of Autism as a spectrum disorder, although the spectrum cannot be clearly defined simply from mild to severe (Kabot et al., 2003). Different children manifest different combinations of symptoms of varying severity although all sharing the core deficit in forming relationship and communication (Kusch & Petermann, 1995) highlighting the complexity of the disorder particularly in relation to reliable diagnosis.

Impairment associated with Autism Wing and Gould (1979) originally suggested that the impairments seen in individual with autism could be described as consisting of a triad Impairment in social abilities and relationships, impairment in verbal and non verbal communication and impairment of imaginative activities.Social impairment The first core feature of autism is qualitative impairment of social interaction and relationships (Hobson, 1989; Mundy & Sigman, 1989; Ungers, 1989; Volkmar 1987). In infant this may be exhibited as rigidity, failure to seek physical comfort from other people (De meyer, 1979), and failure to develop normal attachment to parents and caregivers. They fail to develop reciprocal eye contact and social smiling (Volkmar, 1987). As children with Autism develop, social skill deficits remain (Rutter & Garmezy, 1983). They rarely engaged in peer play (Howlin & Rutter, 1987).Language impairment Poor communicative skills are hallmark of autism (Rutter, 1978). In fact many children with autism never acquire functional language skill. When speech does develop, it is often marked with irrelevant content and stereotyped and repetitive vocalizations. Improper use of language and inability to use language for social communication are more characteristics of autistic language deficit (Howlin & Rutter, 1987). Finally, the ability to sustain conversation and produce spontaneous language is greatly limited in person with Autism (Matson, Sevin et al., 1990).Behavior impairment In children with autism shows hand clapping or arm flapping whenever excited or upset. Running aimlessly, rocking, spinning, toe walking or other odd postures are commonly seen in children with Autism. The play of children with Autism is characteristically rigid and lacking in variety and imagination (Rutter, 1978). Changes in enviroment, such as rearranging furniture, can result in extreme emotional reactions (Kanner, 1951). The final core feature of Autism is abnormal response to sensory stimuli. The children with autism responding with undue distress to low volume sounds or being unable to differentiate between verbal communication and other environmental noises are common.Screening of ASD Empirical studies of toddlers with Autism spectrum disorder had found that intensive, specialized early intervention had resulted in quantifiable gains(Harper et al., 2002; McEachin et al., 1993; Sallow & Groupner, 2005; Schreibman, 2000). In order to maximize the opportunity for specialized early intervention, the early identification and diagnosis of ASD were especially important (American Academy of Pediatrics [AAP], 2006). Recently, the AAP (Johnson et al.,2007) even suggested that it was important for children suspected of ASD to begin intervention services. Early identification studies support the feasibility and validity of early diagnosis, even as early as 2 years (Baird et al.,2000; Robins et al., 2001; Stone et al., 2000). Along with screening studies, retrospective studies of infant videotapes (Baranek, 1999; Osterling & Dowson, 1994; Werner et al., 2000), diagnostic stability studies(Charman & Biard, 2002; Gillberg et al.,1990; Kleinman et al., 2008; Lord, 1995; Stone et al., 1999), and inter rater reliability studies (Klin et al.,2000; Stone et al.,1994) have supported the validity of early diagnosis and have identified symptoms that may be present in the early developmental course of ASD. In addition prospective studies of ASD have been useful in indentifying symptoms present in high-risk infants (such as younger siblings of children with ASD) later diagnosed on the Autism spectrum (Landa et al., 2007; Yirmiya & Ozonoff, 2007; Zwaigenbaum et al.,2007). These studies, which have focused on young infants and toddlers, have provided a picture of the symptoms and patterns of behavior observed in the very early course of the disorder. Screening of ASD can lead to improved early identification and referral for a diagnostic evaluation. All professionals involved in early child care (Pediatricians, Neurologists, Psychiatrists, Psychologists, Audiologists, Language pathologists, Occupational therapist and Physical therapist) should be sufficiently familiar with the signs and symptoms of autism recognize possible indicator(Social, Communicative and behavioral) of the need for further diagnostic evaluation (Filipek et al.,1999).

Different screening instrument for Autism spectrum disorder There are so many Autism specific screening instrument that have been designed for use in field. The screening of autism done in two level (Filipek et al., 1999). The instruments used in level I screening consist of CHAT (Checklist for Autism in Toddler), M-CHAT (Modified Checklist for Autism in Toddler), PDDST-I(Pervasive developmental Disorder Screening Test Stage-I), SCQ(Social Communication Questionnaire) and STAT(Screening Tool for Autism in Two year olds). CHAT (Baron-Cohen et al., 1992; 1996)is a screening test for Autism in children from 18 to 36 months of age, it contains 9 parent questions and 5 behavioral observation items. Absence of three items is considered critical; Protodeclarative pointing Gaze monitoring and Pretend play. It takes 15 minute for completion. It has high specificity but low sensitivity. PDDST-I was developed by Sagel et al. in 2004 which is use full in children between 18-48 month of age. It required 10 minute of time to complete the 22 questions by the parents. The sensitivity and specificity yet not have been clear. The further evaluation required in next stages of same scale. STAT Developed by Stone et al in 2004. It is an interactive play instrument designed for children 24-25 month old. Failure in 2 of 3 areas (Play, Motor imitation, and Non verbal communication) differentiates autism from other developmental problems. It requires 20 minutes time for administration. Its sensitivity is higher than its specificity. When comparing with the above instruments M-CHAT is highly sensitive and specific in the screening for Autism in age of 18-24 months. It was developed by Diana Robins a Psychiatrist in Connecticut in 1999. It consist of 23 yes/no question which is filled by the parents required 5 minute for completion. it is available in so many languages which helps parents to easily understand the content. It is important to realize that parents usually are correct in their concerns about their childs development (Glascoe, 1994, 1997, 1998; Glascoe & Dworkin, 1995). They may not be as accurate regarding the qualitative and quantitative parameters surrounding the developmental abnormality, but almost always, if there is a concern on chief complaint must be valued and lead to further investigation. M-CHAT retained the 9 parent report items from the CHAT and added 14 additional items, based on a survey of the literature and clinical judgment. Six critical items were identified from the 23 items on the M-CHAT they were Protodeclarative pointing, response to name, interest in peers, bringing things to show to parents, following a point, imitation. Children who failed any 3 of 23 total items or 2 of 6 critical items were categorized as at risk for ASD.

The CARS (Childhood Autism Rating Scale) is the level-II screening instrument developed by the Schopler et al., in 1988 in North Carolina. It is a 15-item structured interview and observation instrument which is suitable for use with any child over 24 months of age. Each of the 15 items uses a 7-point rating scale to indicate the degree to which the childs behavior deviates from an age-appropriate norm; in addition, it distinguishes mild-to-moderate from severe autism. The CARS is widely recognized and used as a reliable instrument for the diagnosis of Autism, and takes approximately 30 to 45 minutes to administer (Schopler, Reichler, De Vellis, & Daly, 1980).

NEED OF THE STUDY Autism is a disorder that affects individual across the life span. Early diagnosis required for early intervention. For that sufficient knowledge about the Autism spectrum disorders required to professionals including Physiotherapist (Filipek et al., 1999). The present study was designed to provide concordance data in children with ASD on two commonly used method for screening Autism, the M-CHAT and CARS. The M-CHAT was selected based on its highly specificity and sensitivity as well as it was easy to understand and completion by parents which require 5 minutes for whole process. The CARS was selected based on its well researched psychometric in children (), and its status as the gold standard of Autism rating scales (). The goal of this study was to investigate the correlation between M-CHAT and CARS. These two instruments were developed to screen the same construct Autism spectrum disorder. If these do measure the same construct then one would expect their measure to agree. Understanding of the correlation between instruments was a necessary component to effective assessments which physiotherapist utilize this tool effectively during assessment of pediatric patient and can refer to the0 primary care provider for further evaluation of the same patient with autism who received physiotherapy for delayed development. 9