Research places emphasis on the early diagnosis of the autism spectrum disorder (ASD) as the literature consistently highlights the critical role of early intervention in achieving a more positive prognosis [1,2]. Various screening tools have been proposed and actively employed to promote the earliest possible intervention by measuring the key features of ASD based on Diagnostic and Statistical Manual of Mental Disorders-fifth edition (DSM-5) criteria: persistent and prominent deficits in social interaction/communication and restricted and repetitive behaviors (RRBs) and interests, both presenting from an early developmental period. The Social Responsiveness Scale (SRS) is currently one of the most widely used screening tools for ASD worldwide as it has significant advantages.

By examining the traits highly distinct to ASD, the SRS quantitatively measures the continuum of autism symptom severity [3]. The SRS evaluates the child’s social insight, social information processing, mutual social interaction, social anxiety/avoidance, autistic immersion and characteristics. The SRS offers a good interpretation of ASD’s genetic/neurologic features [4-6], and it has been proven to measure the autistic phenotype transmitted across the generation [7-9], which further solidifies its construct validity and utility as a quantitative measure of ASD traits that conveys the intuitive degree of impairment [10]. As the SRS may be implemented not only by professionally trained practitioners, but also by main caregivers such as parents or teachers, it tends to be less time-consuming and more accessible to children in need as compared to other more formalized diagnostic tools. Another strength of the SRS is that it has been translated and customized into more than 20 official languages and has been employed internationally [11].

As this screening instrument was originally developed in USA and initially validated with the US population [3,12-14], various cross-cultural studies have been conducted aiming to confirm the SRS’s validity and reliability based on each country’s own child population. The SRS has been shown to possess decent psychometric quality when used on large school-based child populations in Germany [15], UK [16], and Iran [17]. The SRS has maintained its validity when employed in clinical and school-based samples in Mexico [18], mainland China [19], Taiwan [20,21], Vietnam [22], and Japan [23]. However, majority of cross-cultural validation in literature have been fairly limited to children and the adolescent group between the ages of 4 to 18 years old, as they were the original target of the standard SRS questionnaire. Few studies have confirmed the validity of SRS among adults internationally [24-26], and even fewer studies have been conducted focusing mainly on the preschooler/toddler group [21,27].

In Korea, to the best of authors’ knowledge, there exists only a single validation study of the Korean version of SRS (K-SRS) focusing on children aged 6 to 12 years old, which showed that the K-SRS has an adequate degree of reliability and validity among Korean participants [11]. While the study reflects results from international validation processes, there has been a lack of Korean studies examining the validity of SRS in age groups beyond the standard age group, such as children and adolescents aged 4 to 18 years old. It is necessary to evaluate the validity of the SRS for younger groups such as toddlers, considering the importance of early diagnosis and intervention of ASD.

Furthermore, overestimating ASD traits may potentially result in the wastage of diagnostic/therapeutic resources, while underestimating may result in the failure to make an early diagnosis; both are possible depending on the cut-off score. Literature has repeatedly pointed out that cultural differences may attenuate the original statistical power of diagnostic tools for ASD, especially for Asian populations [21,23]. Thus, the original SRS cut-off scores recommended by the official U.S. manual may result in less than optimal sensitivity/specificity in the transcultural context, prompting a call for the standardization process and for setting unique cut-off scores for screening based on each cultural/ethnic population [27]. However, there have been no studies that aim to determine a standardized SRS cut-off score for the population of Korean preschoolers and toddlers.

Given this context, this study aims to examine the psychometric properties of the Korean version of the SRS-2 Preschool form, including the questionnaire’s discriminative validity against ASD, other developmental disorders (OD), and the typical development (TD) group among Korean preschool children. Additionally, we determined the best-estimate-cut-off scores for the screening of ASD in Korean preschool children while also conducting a satellite analysis to examine the correlation between the SRS scores of children with ASD and their parents and perform a preliminary exploration on the inheritable end phenotype of ASD, which is the main target of SRS evaluation.

This study is the first to establish the validity of the SRS preschool form when used on Korean children. The mean scores of the SRS were statistically different between the ASD and non-ASD group, and these also significantly differed among the ASD, OD, and TD groups. Adjusting for age did not affect the significance. This may suggest that SRS may be employed not only as a screening instrument to differentiate ASD and non-ASD, but may also aid in the in-depth screening and diagnosis of ASD, supporting the endeavor to detect and differentiate ASD from other development disorders. Another study by the author has also demonstrated the high validity of the Korean ADI-R in ASD detection in comparison with the OD group [42].

Furthermore, the significant difference in SRS mean scores was maintained in the subgroup analysis of children aged below 30 months. The result supports that the SRS preschool form may sustain its diagnostic efficacy in Korean children population even below its original indicated age group, and can thus aid in prescreening procedures for children below 30 months. Considering the importance of making the earliest possible diagnosis and providing intervention in the course of managing ASD [43,44], being able to apply the SRS in an even younger age group may yield great implications for clinical practice.

Our results correspond with literature based on the East Asian preschool population. Stickley et al. [27] employed the Japanese preschool version of the SRS (SRS-P) [39], which is a modified variation of the original SRS and almost identical to the latest SRS-2 Preschool Form intended for children aged between 30 to 54 months [14]. In the study, which included a clinical and community based sample of toddlers between the age of 26 to 51 months in Japan showed a good degree of reliability and validity in terms of SRS-P scores, proving SRS-P’s utility in the process of screening and diagnosing ASD in Japanese preschool children. Our subgroup analysis of children aged below 30 months further validates Stickley et al’s [27] supposition that the autistic end phenotype can be discernible and quantitatively measured at an even earlier age than 2 to 4.5 years old. In an earlier work, Wang et al. [21] employed the original SRS to evaluate a clinical and community based sample of Taiwanese children aged 4 to 6, validating its solid psychometric property to diagnose ASD.

We verified the convergent validity of SRS by identifying relevant correlations of SRS with SCQ and K-CARS. There were positive and significant correlations between SRS and SCQ, and SRS and K-CARS across all age groups, but this correlation was strongest among children aged above 30 months, which was the age group for which the SRS preschool form was originally designed.

According to our analysis, the optimal cut-off score of SRS was 55 for the entire age group, which was substantially lower than the original U.S. cut-off score of 60 which is also currently being employed in the Korean clinical field. The findings support the previous study on the use of SRS on the Korean school age population which found much lower optimal cut-off scores, 52 for males and 51 for females, compared to the U.S. cut-off scores of 70 for males and 65 for females [11]. Based on our results, the direct application of the U.S. cut off score will result in a higher false-negative rate among Korean children, thus deterring early accurate screening and appropriate intervention.

In addition, as SRS is a diagnostic measure which mainly depends on the self-reports of the main caregivers, the difference in the optimal cut-off score may reflect cultural differences or even differing health literacy levels among the caregivers in each country, featuring a wide spectrum of perspectives in the evaluation and classification of children’s behavior as typical or autistic based on their cultural background. The literature has shown consistent differences between the original and Korean cut-off scores in other ASD diagnostic tools. For example, the original cut-off score of K-CARS was 30, but the optimal cutoff score based on Korean data was 28.5 for all participants (sensitivity=0.871, specificity=0.8), and 24.5 for the high-functioning ASD group (sensitivity=0.759, specificity=0.771) [36]. The optimal cut-off score for the SCQ was also lower for Korean children. Compared to the original cut-off score of 15, the optimal cut-off scores were 12 points for children aged 48 months and above, and 10 points for children below 47 months based on Korean data [38]. The consistent lower cut-off scores in Korean data across various screening tools which depend on self-reports may indicate relatively lower recognition of the symptoms or risk signs of ASD [42], or the tendency of Korean caregivers to report the children’s status in a more positive manner and with more caution due to the negative social stigma surrounding behavioral and mental health problems [11]; conversely, they may have a more lenient standards in evaluating the children’s behavior. The findings suggest that the risk of false negative diagnoses is even higher in the Korean children population since the diagnosis is made solely based on the caregivers’ self-reports. A comprehensive evaluation by professionals may have greater implications in this matter.

The SRS has been employed as a surrogate to examine and quantify the relationship of autistic traits within the family in past studies. Constantino and Todd7 showed statistically significant intraclass correlation (ICC) between the SRS scores of children and their parents (mother-daughter=0.41, mother-son=0.38, father-daughter=0.49, father-son=0.58). We also conducted the satellite analysis exploring the correlation between the SRS scores of children and their parents. There was a significant positive correlation between the SRS scores of children and their mothers overall and in the group aged 30 months and below.

However, when we confined the analysis to children with ASD, their scores had no significant correlation with those of their parents. In contrast, there was a weak but significant correlation between the scores of children without ASD with those of both their parents. These results replicate the pattern observed in previous studies. A study by Lyall et al. [8] demonstrated that the parental autistic traits measured through SRS scores can potentially predict the risk of the diagnosis of ASD in their children; however, there was no direct correlation between the SRS scores of children with ASD and their parents (mother-ASD child: r=0.02, ICC=0.0; father-ASD child: r=0.13, ICC=0.0), while there was a moderate degree of correlation between the scores of children without ASD and their parents (mother-non-ASD child: r=0.30, ICC=0.31; father-non-ASD child: r=0.42, ICC=0.33). The lack of a significant correlation between the scores of children with ASD and their parents was further supported by a study conducted by Page et al [9], who also found a strong correlation between the scores of children without ASD and their parents (mother-ASD child: ICC=0.11; father-ASD child: ICC=0.27; mother-non-ASD child: ICC=0.65; father-non-ASD child: ICC=0.68).

The absence of a correlation between the SRS scores of children with ASD and those of their parents has been postulated to be due to the restriction in score ranges in children with ASD compared to children without ASD [8], and further studies are necessary to exclude if there is an additional transcultural impact of parents’ evaluation on themselves. Similar to the case in children, parents may under-recognize or underreport their status due to various cultural norms/backgrounds. Our result, overall, supports the hypothesis that there is a significant correlation between the observable autistic traits in parents and their children which could be more prominently measured in the subsyndromal range across the normal population, and those end phenotypes may be the ramification of genetic inheritability [8,45].

The study has several limitations. First, multiple evaluators conducted the assessment procedures resulting in uncertain inter-rater reliability, which may reduce the accuracy and coherent validity of the entire data. Secondly, there was a relatively small number of participants aged below 30 months with ASD, which may further reduce the statistical validity in the relative subgroup analysis. The optimal cut-off scores in the age group below 30 months notably differed from the other two groups, and had the lowest AUC, sensitivity, and specificity. Lastly, the adult sample was relatively small as well, almost half of the child participants, which may further reduce the statistical power of our satellite study.

In spite of the limitations above, this study provided a rational basis to employ the SRS preschool form for screening and diagnosing ASD among the population of Korean children. The SRS preschool form may also sustain its efficacy under the originally intended age group. Furthermore, the study’s adjusted cut-off scores are much lower than the original scores. The application of these customized cut-off scores, which reflect the transcultural difference, would further increase the diagnostic power of the SRS in the course of ASD evaluation.