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Introduction
Background
Early detection of developmental delays in children is crucial for evaluating
their growth and development. Prompt identification of these delays and the
implementation of appropriate interventions can either lessen their impact or
address underlying causes to support normal development [1–4]. While
accurate assessment of a child’s developmental status typically requires
complex testing by highly trained specialists [5–7], such methods are
too time-consuming and impractical for general pediatric practice. Simpler,
time-efficient screening tests that can be easily administered by pediatricians
are more useful in clinical settings [8–10]. The Denver
Developmental Screening Test (DDST) [11,12] is the most widely
used of these tests and is also employed in Korea. A pediatrician can conduct
this test in about 20 minutes without special training. However, the DDST was
developed based on children in Denver, a city in the United States, and may not
be fully suitable for assessing the development of Korean children.
Methods
Ethics statement
Neither institutional review board approval nor informed consent was obtained for
this study. In 1985, systems for ethical oversight, such as ethics statements,
were not yet established in Korea.
Study design
This validity study was aimed at adapting a measurement tool originally developed
in the United States for use in Korea.
Setting
From July 1985 to September 1986, a period of approximately 14 months, the DDST
was administered to 2,140 children, both boys and girls (Tables 1, 2). The
DDST manual and test forms [13] were
translated into Korean and underwent several revisions (Supplement 1). Examiners
were thoroughly trained using the translated materials through repeated
explanations, discussions, and demonstrations. After the test was administered
to 32 children, inter-examiner reliability was established. To ensure the
accuracy of the results, two examiners worked as a team: one administered the
test while the other recorded the results.
Table 1.
Distribution of sample by age
Participants
Children ranging in age from 2 weeks to 6 years and 4 months, as defined by the
DDST, were included in the study. The participants were selected from those
attending pediatric departments and child counseling centers at Ewha University
Hospital, Red Cross Hospital, National Medical Center, Hanyang University
Hospital, and Bangzi Hospital. In accordance with DDST guidelines, we excluded
premature infants, twins, breech deliveries, adopted children, and children with
visual or hearing impairments, central nervous system disorders, cleft palate,
Down syndrome, or any acute or chronic illnesses. The team of examiners
consisted of 15 individuals, including the researcher, medical students,
pediatric residents, and students majoring in early childhood education.
Data sources/measurement
The testing materials used aligned with those specified in the manual. However,
certain test items were modified, as follows.
In the language domain, “Uses plurals” was excluded because plural
and singular forms are not distinguished in spoken Korean. For “Defines
words,” the passing criterion was adjusted from correctly defining six
out of nine words to three out of nine. In “Object drawing,” a
child was considered to pass if at least one of the three items was correct,
rather than requiring all three to be correct. These modifications were based on
preliminary studies that revealed differences in language expression among
Korean children. Similar adjustments were made in the development of the
Japanese version of the DDST [14].
Reliability and validity were evaluated. Prior to beginning the study,
inter-examiner reliability was established. One examiner administered the test
while another observed and independently recorded the results; then, the level
of agreement was calculated. Overall, 32 children, ranging in age from 3 months
to 5 years, were assessed to determine reliability. The inter-examiner
reliability scores varied from 93.8% to 100%, with an average of 97.3%.
To assess validity, the DDST was administered to 30 children ranging in age from
3 months to 5 years. Subsequently, these children were evaluated using either
the Bayley Scales of Infant Development or the Korea University–Binet
Intelligence Test [15]. As shown in Table 3, all three children who scored an
intelligence quotient of ≤75 or ≤69 on these respective tests were
rated as either “questionable” or “abnormal” on the
DDST, demonstrating high concordance despite the small sample size.
Results
Participating children
The DDST was administered to a total of 2,140 boys and girls. Tables 1, 2 detail the distributions of their ages and sexes. The occupational
distribution of the participants’ fathers (Table 4) did not significantly differ from that of the
general population in Seoul, as recorded in the 25th Seoul Statistical Yearbook,
published in December 1985 (P>0.05).
Table 4.
Occupations of fathers of participants compared with the general population of Seoul
| Occupation | Sample (%) | Seoul general population (%)1) |
|---|---|---|
| Administrative, managerial, or professional | 13.1 | 11.9 |
| Clerical and related workers | 40.4 | 22.7 |
| Commerce | 21.3 | 25.6 |
| Service | 4.3 | 8.7 |
| Agriculture, livestock, forestry, fishery | 0.6 | 0.7 |
| Production, transportation | 23.5 | 30.9 |
| Unknown, military, student, unemployed | 7.5 | 0 |
Main results
Results of test items by city
The ages at which 25%, 50%, 70%, and 90% of children passed each of the 104
test items (Supplement
2) were calculated. These findings were then compared with the
results of children from Denver and Tokyo. A difference exceeding 20% was
considered significant. The percentage difference was determined using the
following formula:
Comparison between children in Seoul and Denver
Test items exhibiting a difference of more than 20% are compared in Supplement 3.
Personal-social domain: For 10 of the 23 items, children from Seoul
demonstrated more rapid development than their counterparts from Denver.
Both 50% and 90% passing ages were earlier for four items: “Resists
when a toy is taken away,” “Plays peek-a-boo,”
“Attempts to reach distant toys,” and “Plays
ball.” Only one item, “Easily separates from mother,”
was achieved earlier by the Denver children.
Fine motor-adaptive domain: Of the 30 items, relative to their counterparts
from Denver, children from Seoul demonstrated faster development for eight.
This was evident in both 50% and 90% passing ages for three items:
“Regards raisin,” “Picks up raisin with thumb and
forefinger,” and “Copies a square.” Conversely, the
Denver group exhibited more rapid development for three items.
Language domain: Of the 20 items, children from Seoul demonstrated faster
development than the Denver children in seven. These items included
“Says ‘mama,’ ‘dada’
(non-specific),” “Turns head to voice,” and
“Follows simple commands.” The item “Defines
words” was not included in the comparison due to changes in the
scoring criteria.
Gross motor domain: For seven of the 31 items, children from Seoul
demonstrated more rapid development than those in Denver. They reached both
the 50% and 90% passing ages more quickly for “Bears weight on legs
when held upright” and “Head lag disappears when pulled to
sit.” The Denver children did not exhibit faster development for any
items.
Comparison between children in Seoul and Tokyo (Supplement 4)
Personal-social domain: Children from Seoul demonstrated faster development
for 11 of the 23 items, reaching both the 50% and 90% passing ages more
quickly for five of these items. The children from Tokyo outpaced their
Seoul counterparts for only one item.
Fine motor-adaptive domain: Children from Seoul displayed faster development
for 12 of the 31 items, reaching both the 50% and 90% passing ages earlier
for three items. The Tokyo group exhibited more rapid development for one
item.
Language domain: Children from Seoul exhibited faster development for 10 of
the 20 items, reaching both the 50% and 90% passing ages earlier for two
items. The Tokyo children displayed more rapid development for two
items.
Gross motor domain: Children from Seoul demonstrated faster development for
14 of the 31 items, attaining both the 50% and 90% passing ages earlier for
six items.
In Supplement 5, we
superimposed the average ages of children from Seoul onto the original DDST
chart to facilitate direct comparison with children from Denver. Dark
shading on the left side of the bar indicates that the Seoul children
achieved a milestone earlier, while shading on the right side signifies
later achievement. As shown, the children from Seoul were ahead in many test
items across all four domains and age groups.
Supplement 6
presents the Korean version of the DDST, developed based on the average data
from the children in Seoul (Supplement 2). This version can replace the original
DDST for the developmental screening of Korean children and should be used
in conjunction with standardized testing materials and appropriate training.
As explained, the Korean children demonstrated more rapid development for
many test items across all domains and ages.
Discussion
Key results
In this study, the DDST was administered to 2,140 boys and girls ranging in age
from 2 weeks to 6 years and 4 months, all residing in Seoul. When comparing the
results with those from Denver and Tokyo, children from Seoul demonstrated more
advanced development in multiple test items across all four developmental
domains. Specifically, they were ahead in 10 out of 23 items in the
personal-social domain, eight out of 30 items in the fine motor-adaptive domain,
seven out of 20 items in the language domain, and seven out of 31 items in the
gross motor domain. These differences were observed across all age groups.
Interpretation/comparison with previous studies
Developmental delays in children can arise from various causes, including
congenital or genetic disorders, complications during childbirth, and
environmental factors after birth. Early detection is crucial for identifying
the underlying causes and initiating interventions that can mitigate delays.
Detection also enables parents to understand the delay and thus engage in more
constructive childcare and educational practices [1–4,9].
Historically, a variety of methods have been developed to assess child
development, each with advantages and disadvantages. Many of these methods are
complex and time-consuming, rendering them impractical for use by general
pediatricians [5–7]. Consequently, simple screening tests for
developmental delays have been emphasized [8–10,16].
The DDST [11–13,17–19] is the most widely used screening tool.
General pediatricians, nurses, or medical students can administer the DDST
without specialized training, and it takes only 15–20 minutes to
complete. This instrument was developed based on a population of children from
Denver, and while it has been claimed to be applicable in other regions, studies
have indicated differences among children from other countries [20–26], as detailed below.
Cardiff: A study by Bryant et al. [20]
revealed that infants in Cardiff exhibited advanced development in the
personal-social and language domains but delays in gross motor development
compared to their counterparts in Denver. Employing the original DDST could thus
lead to the misclassification of normal gross motor development as delayed
[27].
Tokyo: Ueda [26] observed that infants in
Tokyo display relatively delayed gross motor development and preschool children
exhibit delayed language development, which can be attributed to environmental
factors such as childcare practices. For instance, Japanese infants are often
not placed in a prone position, potentially leading to delays in the ability to
lift the head or chest.
Hong Kong: A study by Fung and Lau [21]
indicated that Chinese infants in Hong Kong exhibited delayed gross motor
development, which normalized post-infancy. Contributing to this delay were
cultural practices such as swaddling and a tendency towards overprotective
parenting.
Differences stemming from childcare methods have also been observed in African
[24,28] and Mexican infants [23].
Furthermore, economic factors can affect development; children from low-income
families may exhibit delays in language and conceptual thinking tasks [29,30].
In this study, children from Seoul exhibited more rapid development across all
domains compared to their counterparts in Denver and Tokyo. This trend was
observed consistently among age groups. Two aspects of Korean childcare
practices may contribute to this phenomenon. First, close physical contact is
near-constant; Korean mothers often maintain close physical contact with their
infants, frequently carrying or holding them, even during sleep. Sensory
stimulation through skin-to-skin contact is known to facilitate development
[4,31]. Second, a high value is placed on education. Korean parents
emphasize educational achievement, providing educational materials at an early
age and enrolling their children in preschools and academies. Nonetheless,
genetic factors could also play a role in development, warranting further
investigation.
Given the numerous test items for which Seoul children outperformed their
counterparts, applying the original DDST to Korean children is unsuitable, as
children with developmental delays could be misclassified as developmentally
normal. The occupations of the fathers in our sample were comparable to those of
the broader population of Seoul (Table
4), and the inter-examiner reliability was high. Validity tests
demonstrated high concordance with established developmental scales (Table 3). Therefore, the establishment of a
Korean version of the DDST based on our results is justified.
Accordingly, we developed the Korean version of the DDST (Supplement 6), tailored
to the assessment of Korean children. Adequate training and standardized
administration are essential for accurate results.
Limitations
This study has several limitations. First, it was restricted to children visiting
specific institutions in Seoul, which may not be representative of the broader
pediatric population of the city. Second, children who visit hospitals and
counseling centers might not fully reflect the health status of the general
pediatric population, potentially impacting the generalizability of the
findings. Third, the sample sizes for testing inter-examiner reliability (32
children) and validity (30 children) were relatively small, possibly affecting
the statistical reliability of the results.
Conclusion
Using the DDST, we examined the developmental progress of 2,140
children—both boys and girls—ranging in age from 2 weeks to 6
years and 4 months. The following results were obtained.
Overall advancement: Children in Seoul exhibited faster development than their counterparts in Denver and Tokyo across all domains and age groups.
Personal-social domain (23 items): Children from Seoul displayed slower attainment of only one item compared to both Denver and Tokyo children, while they exhibited faster development regarding 11 items.
Fine motor-adaptive domain (30 items): Compared to children in Denver, those in Seoul exhibited slower development regarding three items and faster development for eight. Compared to children in Tokyo, they were slower for one item and faster for 12.
Language domain (20 items): Children from Seoul displayed more rapid development for seven items compared to children from Denver. Relative to their counterparts in Tokyo, the Seoul group exhibited slower development for two items and faster attainment for 10.
Gross motor domain (31 items): Children from Seoul exhibited faster development for seven items compared to their counterparts in Denver and for 14 items compared to children from Tokyo.
The findings indicate that environmental factors and ethnic differences may
contribute to the accelerated development observed in children from Seoul. To
address these distinctions, we have developed and presented a Korean version of
the DDST, which was informed by the study results. This research is anticipated
to aid in the early detection of developmental delays and the implementation of
appropriate interventions by offering an assessment tool tailored to the
developmental evaluation of Korean children.
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