Since repetition of actions serve the purpose of skill acquisition and mastery, as development progresses and mastery of skills is attained, RRBs reduce overtime in typically developing children . Specifically, studies have found consistent patterns of certain repetitive behaviors present in the first year, increase until roughly the age of three and start to decline around the fourth year . This reduction in repetitive behaviors over time has been found in studies using parent report measures of children in the first four years of life , as well as observational coding of repetitive behaviors in young children .Studies involving early developmental behaviors face the obstacle of the fluctuations that naturally occur in development, making the measurement of behaviors an important factor to consider. Specifically for RRBs, the type of repetitive behaviors captured, environmental influences such as location or caregiver presence, and the measurement tool used can all influence results. Thelen examined body stereotypies of 20 infants in the first year using live behavioral observations across contexts such as feeding, interactions with caregivers and while the infants were interacting with objects. Thelen collected data on bouts of rhythmical body movements including movements of the legs , torso and arms . While stereotypies decreased over time, contextual triggers impacted the type of body stereotypies observed. Patterns in stereotypies were found to increase when the infants were interacting with their caregivers, dutch buckets system and while in a heightened state of arousal. Understanding contextual dependency and fluctuations within the TD population will help to inform similar behaviors observed in children with ASD.

It has been posited that in the case of caregiver interactions, increased stereotypies may serve a communicative function; that is, kicking and bouncing rhythmically may serve communicative value to express pleasure and excitement. These differences found in frequency of stereotypies when a caregiver is present highlights the importance of measurement, and for many behaviors, parent report may be the most inclusive tool to better understand the presence of atypical behaviors across contexts. Understanding the developmental pattern, frequencies and types of RRBs in typically developing children is informative in determining what constitutes atypicality of RRBs for children with ASD. The repetition of behaviors observed in typically developing infants andtoddlers exhibit overlap with the behaviors indicating developmental concern or impacting diagnostic outcomes in children with ASD. Unfortunately, information is somewhat limited on the presence, severity and developmental pattern of specific RRB subtypes longitudinally. More often, studies have examined the role of RRB presentation in differentiating children with ASD from other clinical or control groups. Findings have indicated that in contrast to the pattern found for TD children of RRBs peaking around 2 and dissipating by 4, children with ASD exhibit a continual increase in the frequency and severity of RRBs through late childhood . The organization, division and measurement of RRBs inevitably influence findings; such methodological inconsistencies have pervaded RRB research and limited understanding of complicated relationships between RRBs and other individual characteristics . A variety of approaches have been taken to organize and operationally define RRBs in ASD. In order to build upon advances made in RRB research, it is essential to consider the methodological approaches taken .The decision to include or exclude certain RRB types significantly influence results, leading to inconsistencies across studies purely based on methodological limitations. Therefore, in order to sufficiently understand and improve this area of research, researchers must evaluate the organization, inclusion and exclusion of RRBs, which vary by study.

As Troyb points out, findings vary based on the behavior included, with inconsistent results between RRBs and, for example, functioning level, based on the RRB types examined. The most commonly used organization, definition, and measurement of RRBs will be described further.Dichotomization of behaviors into low-level and high-level RRBs is one of the most common organizational approaches . An alternative label for these two categories are Repetitive Sensory Motor behaviors for low-level RRBs and Insistence on Sameness for high-level RRBs . This approach of dichotomizing RRBs is nearly identical, therefore low level and RSM can be used interchangeably, and the same applies to high-level and IS behaviors. Low-level RRBs include repetitive motor stereotypies such as hand flicking, body rocking, etc., stereotyped or repetitive speech vocalizations, and repetitive actions with objects such as spinning wheels, repetitively opening and closing containers, etc. These behaviors may also possess sensory components, implying a physiological function may be simultaneously served while children engage in certain RRBs . RRBs conceptualized as low-level are often associated with younger and lower functioning children, yet are also present in early typical development and in other developmental and psychiatric conditions such as Fragile-X syndrome, Rett syndrome and Tourette’s syndrome . High-level behaviors encompass behaviors such as intense preoccupation with a restricted interest, ritualized behavior patterns, and excessive adherence to routines with significant resistance to change . The most commonly described high-level RRBs include behaviors such as rituals and routines, which make up insistence on sameness behaviors . These rigid behavioral patterns were documented in the original description of ASD as a staple of the unique features of the disorder .

High-level behaviors are commonly associated with older and higher functioning children, when children are more likely to be able to communicate and share intense and perseverative interests, commonly referred to as circumscribed interests, with others . It is possible for multiple subtypes, that is, across high and low level RRB classifications to take place simultaneously, further complicating the measurement and recognition of each RRB presentation . Despite the popularity of this simple shorthand to group behaviors, it has been cautioned that this approach is too broad and may obscure important differences between the many types of RRBs . RRBs have been organized in a number of ways; however differences among how studies categorize behaviors reduce comparability of results. Results are dependent upon the measurement tools used to organize and define various RRB subtypes; therefore it is important to understand the strengths, weaknesses, inclusion and utility of common measurement tools in exploring patterns of RRBs among individuals. The diagnostic criteria for autism spectrum disorder has recently been altered to a dyad of impairments in the domain of social communication ability and the presence of atypical restricted and repetitive behaviors ; American Psychiatric Association, 2013. As the manual for defining and diagnosing a range of disorders, the DSM’s definition of ASD symptomology is important to consider in conceptualizing definitions and measures of RRBs in ASD. The DSM-5 categorizes RRBs into four domains, children must manifest at least two of the following: stereotyped or repetitive speech, motor movements, or use of objects; excessive adherence to routines, ritualized patterns of verbal or nonverbal behavior, or excessive resistance to change; highly restricted, fixated interests that are abnormal in intensity or focus; and hyper- or hypo- reactivity to sensory input or unusual interest in sensory aspects of their environment.The methodological inconsistency across studies is often due to the current lack of a consistent and universal measurement of RRBs. Measurement tools dictate the operational definitions employed, methodological variability in data and analysis between studies, and results found between RRBs and related characteristics . Parent reports have been the most prevalent form of measuring RRBs in children with ASD, which vary across studies. Autism Diagnostic Interview- Revised . The ADI-R is a parent report measure designed to capture developmental history as well as current symptom presentation of individuals with ASD. The three domains the ADI-R addresses are: language and communication, reciprocal social interaction, and restricted,repetitive, and stereotyped behaviors. Each of the three domains has a cut-off score, providing a diagnostic algorithm, which is accurate in differentiating an ASD diagnosis from other disorders. Even though the ADI-R is not intended to independently and all-inclusively measure RRBs, a number of studies have characterized RRBs in individuals with ASD using the RRB sub-scale of the ADI-R . The RRB domain of the interview includes information on both what the child has displayed in the past as well as what behaviors the child is currently exhibiting. Most commonly, studies examining RRBs using this measure exclusively use the “current” items only . Notably, evidence for the dichotomy of high and low-level RRBs were derived from studies that used the ADI-R as their measurement of RRBs; therefore, dutch buckets it hasn’t been unanimously established if that organizational approach is applicable to all individuals with ASD, or if the dichotomy is due to the factor structure of the ADI-R . Despite it’s popularity, there is also methodological concern when studies use a measure for multiple purposes; as the intended use for the ADI-R is to measure a continuum of ASD characteristics and determine diagnostic eligibility. Therefore, utilization of a measurement tool solely for the purpose of measuring RRBs with established validity, reliability and inclusion of all subtypes of RRBs would likely produce a stronger tool for quantifying RRBs. Repetitive Behavior Scale- Revised . The RBS-R is a questionnaire that was designed for the purpose of exclusively measuring a variety of RRBs.

The measure includes 43 items that are rated on a four-point Likert scale across 6 sub-scales, which were conceptually derived and reported by the primary caregiver. The original sub-scales include: stereotyped behavior; self-injurious behavior, compulsive behavior, ritualistic behavior, sameness behavior, and restricted behavior. Since it’s conception, several factor analytic studies have been conducted with the RBS-R with varying results, implying that the original factor structure of 6 sub-scales is not statistically supported based on these results . Lam & Aman were the first to independently explore the factor structure of the RBS-R. They examined data from 307 participants and explored a large age range of individuals with ASD . Results indicated that the RBS-R provides five factors, which overlap with five of the six original scales; the Ritualistic sub-scale, originally proposed by Bodfish, et al. , was the only scale not included in the new factor solution. This finding was supported in a subsequent study of 712 individuals ranging from 2 to 62 years old, which explored the five-factor model . Additionally, Mirenda, et al. used a confirmatory factor analysis to compare several different proposed structure models and found the best models were the Lam & Aman five-factor model and a three factor model . Most recently, Bishop, et al. explored the relationship between ADI-R scores and RBS-R relating to the construct validity of using the RSM and IS dichotomy for RRBs in over 1,800 individuals with ASD. Results from the initial exploratory factor analysis of the RBS-R were similar, with slight divergence in items factor loadings from previous investigations and from the original RBS-R factors . In consideration of the varying results across studies, further exploration of the RBS-R factors is warranted. Organization and measurement of RRBs is a complicated undertaking, with inevitable influence on outcomes when examining the relationship between RRBs and other developmental characteristics . Therefore, advances in understanding the complicated relationships between RRB presentation, chronological age, cognitive functioning, and other developmental skills have progressed more gradually. However, incremental advancement is logical given the complexity and difficulty in RRB measurement. Despite the complexity of RRB presentation and the numerous issues in organization and measurement described, careful evaluation of the phenotypic patterns and related characteristics found warrants further consideration.The relationship between age and RRB presentation in ASD has most commonly been examined through the use of cross sectional data analysis . Researchers have found that that younger children with ASD exhibit higher frequency of low-level RRBs such as motor stereotypies and sensory related behaviors; whereas older, higher functioning individuals on the spectrum tend to exhibit more high-level RRBs, with reduction in low-level RRBs . Specifically, Militerni, et al. found that toddlers exhibited significantly fewer RRBs than older children ; though, this was only true for sensory and motor RRBs , which were significantly less prevalent in the older group. However, the older children were not devoid of RRBs, they instead displayed more complex RRBs such as routinized schedules and insistence on sameness. The developmental trajectories of children with ASD are complex in their symptom presentation across time, further complicated by the manifestation of various types of RRBs. There have been several studies to examine RRB presentation overtime, with varying results across studies . The most common finding in regards to age and RRBs has been an overall reduction overtime in RRBs, with a more significant decrease overtime in low-level RRBs such as repetitive object use or motor actions .