Prevalence of Selected Developmental Disabilities in Children 3-10 Years of Age: the Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991

Coleen A. Boyle, Ph.D. Marshalyn Yeargin-Allsopp, M.D.

Nancy S. Doernberg Patricia Holmgreen, M.S. Catherine C. Murphy, M.P.H.

Diana E. Schendel, Ph.D.

Division of Birth Defects and Developmental Disabilities

National Center for Environmental Health

Abstract

Problem/Condition: Serious developmental disabilities affect approximately 2% of school-age children and are lifelong conditions that incur substantial financial and societal costs.

Reporting Period: January 1991-December 1991.

Description of System: The Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) monitors the prevalence of four serious developmental disabilities -- mental retardation, cerebral palsy, vision impairment, and hearing impairment -- among children 3-10 years of age in the five-county metropolitan-Atlanta area. Children who have at least one of the four developmental disabilities are ascertained through annual review of records at schools, hospitals, and other sources.

Results and Interpretation: During 1991, rates for mental retardation varied by age, race, and sex; rates ranged from 5.2 per 1,000 children to 16.6 per 1,000 children. Regardless of the absolute rate of mental retardation in each of the age-, race-, and sex-specific categories, severe mental retardation (i.e., an intelligence quotient of <50) accounted for one third of all cases. The overall crude rate of cerebral palsy was 2.4 per 1,000 children; however, the rate was higher among black children (3.1 per 1,000 children) than among white children (2.0 per 1,000 children). The rate of moderate to severe hearing impairment was 1.1 per 1,000 children, and the rate of vision impairment was 0.8 per 1,000 children. Rates of hearing impairment were higher among black males than among children in the other race and sex groups, whereas rates for vision impairment varied only slightly between these groups. The rates of the developmental disabilities were not adjusted for possible confounding factors (e.g., maternal education, family income, and various medical conditions). Consequently, the variation in rates may reflect social or other characteristics unique to the study population.

Actions Taken: MADDSP data will be used to direct early childhood intervention efforts to reduce the prevalence of these four developmental disabilities. MADDSP data also are being used to measure progress toward the year 2000 national objectives for the prevention of serious mental retardation.

INTRODUCTION

Since 1968, CDC has conducted surveillance for birth defects (i.e., structural malformations and genetic diseases) in the five-county metropolitan-Atlanta area (1). However, those birth defects that generally are evident at birth (e.g., cleft palate and spina bifida) represent only part of a spectrum of developmental problems that appear during childhood. Other conditions (e.g., mental retardation, autism, and cerebral palsy) usually are manifested after infancy and may be sufficiently severe to require specialized medical and educational services for many years (2). Such conditions are referred to as developmental disabilities.

To address the problem of developmental disabilities among children, CDC and the Georgia Department of Human Resources initiated the Metropolitan Atlanta Developmental Disabilities Study in 1984. For this study, which was conducted in Atlanta during 1985-1987, investigators devised methods for determining the prevalence of mental retardation, epilepsy, cerebral palsy, blindness, and hearing impairment among children 10 years of age (3). Children who had these conditions were identified by searching record systems of sources that were likely to contain information relating to the evaluation or treatment of children who have developmental disabilities (e.g., schools, hospitals, and state programs for persons who have developmental disabilites). The majority of the children were identified through special-education departments within the Atlanta-area public school systems. The success of this study prompted CDC to establish the Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) in 1991, an ongoing system for monitoring the occurrence of selected developmental disabilities.

The two principal objectives of MADDSP are to a) provide regular and systematic monitoring of prevalence rates for selected developmental disabilities according to various demographic characteristics of children and their mothers (which is the focus of this report) and b) provide a framework for initiating special studies of children who have the selected developmental disabilities by establishing a population-based case series of such children. In the future, MADDSP data will be used to measure progress toward the year 2000 national objectives (4) for the prevention of serious mental retardation.

METHODS

MADDSP was established to ascertain all children who have one or more of four developmental disabilities -- mental retardation, cerebral palsy, hearing impairment, and vision impairment -- in the five-county (i.e., Clayton, Cobb, DeKalb, Fulton, and Gwinnett) metropolitan-Atlanta area. In 1990, this area had an estimated population of 2.2 million persons, 39,000 births, and 249,500 children 3-10 years of age. This area has an active birth defects surveillance program -- the Metropolitan Atlanta Congenital Defects Program, which is operated by CDC. Consequently, additional medical data can be obtained by linking the children identified through MADDSP to the birth defects registry.

As a consequence of the Individuals with Disabilities Education Act * (5), most children eligible for MADDSP are either enrolled in special education programs at nine public school systems serving the study area or enrolled in other Georgia Department of Education programs for children who have developmental disabilities (e.g., state schools for children who are hearing or vision impaired and regional psychoeducational centers) (5). Additional sources used to identify children who are eligible for inclusion in MADDSP include a) Georgia Department of Human Resources facilities that provide services for children who have developmental disabilities and b) two metropolitan-Atlanta-area pediatric-care hospitals, one public hospital, and the clinics associated with these facilities.

Source records (e.g., medical and school records) are reviewed annually for children who are potentially eligible for inclusion in the surveillance program. Because most cases of these developmental disabilities are considered lifelong conditions (3), children who have been included in MADDSP in a previous year are included in current year prevalence rates if they still meet age and residence requirements. A child's record is re-examined (on the basis of a time schedule that considers the child's age and underlying diagnosis) to verify and update the child's diagnostic information.

Case Definition

For the purposes of MADDSP, a case is defined as a child a) who is 3-10 years of age at any time during the study year of interest; b) whose parent(s) or legal guardian(s) reside in the five-county metropolitan- Atlanta area during the study year of interest; and c) who has one or more of the four developmental disabilities. The age range of 3-10 years was chosen because the lower boundary (i.e., 3 years of age) corresponds to the beginning of the age span covered by Part B of the Individuals with Disabilities Education Act (5), and the upper boundary (i.e., 10 years of age) is the age at which most children served under the Act should have entered special education programs.

Developmental Disability Definitions

1. Mental retardation is (for the purposes of this surveillance program) a condition marked by an intelligence quotient (IQ) of less than or equal to 70 on the most recently administered standardized psychometric test. In the absence of an IQ-test score, a written statement by a psychometrist that a child's intellectual functioning falls within the range for mental retardation is acceptable. The severity of mental retardation is defined according to the following International Classification of Disease, Ninth Edition, Clinical Modification (ICD-9-CM) categories: mild (an IQ of 50-70), moderate (an IQ of 35-49), severe (an IQ of 20-34), and profound (an IQ of <20) (6).

2. Cerebral palsy is a group of nonprogressive, but often changing, motor impairment syndromes secondary to lesions or anomalies of the brain arising at any time during brain development (7). For this surveillance system, the definition includes postnatally acquired cerebral palsy diagnosed before 11 years of age. Children are included in the surveillance system if they have been a) diagnosed as having cerebral palsy by a qualified physician or b) identified by other qualified professionals (e.g., physical and occupational therapists) as having this disability on the basis of physical findings noted in source records. Cerebral palsy is categorized as "disabling" or "nondisabling" on the basis of the degree of the affected child's ambulation and use of assistive devices (8). Children who have nondisabling cerebral palsy are fully ambulatory and do not require the use of assistive devices, whereas children who have disabling cerebral palsy require the use of assistive devices for ambulation (either intermittently or at all times).

3. Vision impairment is a measured visual acuity of 20/70 or worse, with correction, in the better eye. In the absence of a measured visual acuity, a child is considered visually impaired if a source record includes a) a functional description, by an eye specialist, of visual acuity of 20/70 or worse or b) a statement by an eye specialist that the child has low vision or blindness. Severity of visual impairment is defined using the following ICD-9-CM categories: moderate visual impairment (corrected visual acuity of 20/70-20/160), severe visual impairment (corrected visual acuity of 20/200-20/400), and profound, near total, and total visual impairment, which were grouped together (corrected visual acuity of 20/500 or worse) (6).

4. Hearing impairment is a measured, bilateral, pure-tone hearing loss at frequencies of 500, 1,000, and 2,000 hertz averaging 40 decibels (dBs) or more, unaided, in the better ear. In the absence of a measured, bilateral hearing loss, children meet the case definition if their source records include a description, by a licensed or certified audiologist or qualified physician, of a hearing loss of 40 dBs or more in the better ear. For this program, severity was defined on the basis of the following hearing impairment levels (measured in the better ear): moderate (a hearing loss of 40-64 dBs), severe (a hearing loss of 65-84 dBs), and profound (a hearing loss of greater than or equal to 85 dBs) (9).

Data Collection

In addition to a standard list of demographic variables and identifying information, MADDSP collects both the earliest and most recent evaluation data relevant to the child's specific disabilities. For example, for children whose disability meets the case definition for mental retardation, scores on both the earliest and most recent tests of cognitive functioning are recorded, whereas for those whose disability meets the definition for hearing impairment, both the earliest and most recent hearing level in each ear and the type of hearing loss are recorded. Information concerning associated medical conditions (e.g., chromosomal defects or unintentional injuries) that may be associated with the etiology of the developmental disability is also collected. Data are collected for race because of previously reported race-specific differences in the prevalences of these disabilities (10). Race is obtained from source records.

Analysis

The 1990 U.S. Census data were used to calculate point-prevalence rates for 1991 for children 2-9 years of age (who were 3-10 years of age in 1991) in the five-county metropolitan-Atlanta area. Both the overall rate of each developmental disability and rates by level of severity were calculated. Rates were calculated by race (i.e., white and black), sex, and age. Other race groups were not included in this report because of the limited number of reported cases among other races. Age represents the age the child reached in 1991.

Point-prevalence rates were calculated rather than birth-cohort prevalence rates (or ratios) because they represent the burden of disease in the population at one particular time (11). Moreover, these rates are the more appropriate measure for the data collected because they reflect all cases rather than the subset involving children who were born in the study area. Children were counted in more than one rate if they had more than one of the four disabilities.

RESULTS

In metropolitan Atlanta during 1991, a total of 2,692 children were identified as having one or more of the four developmental disabilities. Eighteen percent of these children had more than one developmental disability, representing a total of 3,295 disabilities.

Source of Ascertainment

With the exception of children who had cerebral palsy, >90% of children who had developmental disabilities were identified through one of the Georgia Department of Education sources. Among children identified as having cerebral palsy, 17% were identified from hospital records, and 7% were identified from a Department of Human Resources' source.

Mental Retardation

The overall prevalence of mental retardation was 8.7 per 1,000 children 3-10 years of age, and approximately two thirds of cases were of mild severity (Table_1). The prevalence of mental retardation varied with age, increasing from 5.2 per 1,000 children 3-4 years of age to 12.3 per 1,000 children 9-10 years of age. This increase in reported prevalence with advancing age occurred among children who had mild and moderate mental retardation but not among those who had severe or profound mental retardation; for these categories, the rate was relatively constant with advancing age.

Rates of mental retardation for black males were 3.1, 2.4, and 1.7 times higher than rates for white females, white males, and black females, respectively (Table_2). This pattern was found within each level of mental retardation, with the exception of profound mental retardation. In each of the sex-race-specific groups, regardless of the absolute rate of mental retardation, two thirds of the children were in the mild range.

Cerebral Palsy

The overall rate of cerebral palsy was 2.4 per 1,000 children 3-10 years of age (Table_3). An age-specific pattern was evident -- the youngest children had the lowest prevalence rates, and children in the middle age range (i.e., 5-6 years of age) had the highest rates; this pattern was found for disabling, but not for nondisabling, cerebral palsy.

Rates of nondisabling cerebral palsy were higher for black children than for white children (Table_4). Although a similar disparity between races occurred among children with disabling cerebral palsy, the magnitude of the difference was considerably less. Black females and black males had similar rates of both disabling and nondisabling cerebral palsy. Compared with white males, white females had lower rates of nondisabling cerebral palsy but similar rates of disabling cerebral palsy.

Eleven percent of the children who had cerebral palsy (N=58) had a postnatal cause for their disability, resulting in a prevalence of 0.2 per 1,000 children for acquired cerebral palsy and 2.2 per 1,000 children for congenital cerebral palsy. Eighty-three percent of all children who had cerebral palsy had spastic cerebral palsy, 2% had dyskinetic cerebral palsy, 1% had ataxic cerebral palsy, and 7% had other types of cerebral palsy. The type of cerebral palsy could not be determined from the available records for 7% of affected children.

Hearing Impairment

The overall prevalence of hearing impairment was 1.1 per 1,000 children 3-10 years of age, and the rate increased steadily with age (Table_5)

• a trend that generally was found for all severity levels. Overall rates of hearing impairment were higher for black males than for other race and sex groups (Table_6). The predominant type of hearing impairment was sensorineural (79%), followed by conductive hearing impairment (6%), and both sensorineural and conductive combined (3%). The type of hearing loss was unknown for 12% of children.

Vision Impairment

The overall prevalence rate for vision impairment was 0.8 per 1,000 children 3-10 years of age. The prevalence of vision impairment increased with age up to the age of 7 years and then leveled off (Table_7). This pattern was observed for all severity levels of vision impairment. The prevalence of vision impairment was similar among the various race- and sex-specific subgroups of children (Table_8).

Coexisting Developmental Disabilities

Seventy-three percent of children who had vision impairment and 66% of those who had cerebral palsy met the case definition for one of the other developmental disabilities included in MADDSP (primarily mental retardation and vision impairment for children who had cerebral palsy and mental retardation and cerebral palsy for children who had vision impairment) (Table_9). In contrast, only 22% of children who had mental retardation and 23% of children who had hearing impairment had coexisting conditions (primarily cerebral palsy for children who had mental retardation and mental retardation for children who had hearing impairment).

Age at First Diagnosis

Only 10% of children who had mental retardation, 35% of children who had cerebral palsy, 17% of those who had hearing impairment, and 17% of those who had vision impairment were first diagnosed before 2 years of age. Children who had more severe forms of a developmental disability generally were diagnosed at an earlier age. For example, 36% of children who had profound mental retardation were identified before the age of 2 years compared with only 7% of children who had mild mental retardation. However, by 5 years of age, 67% of children who had mental retardation, 87% of children who had cerebral palsy, 83% of children who had hearing impairment, and 70% of children who had vision impairment had been identified.

DISCUSSION

Developmental disabilities are lifelong conditions that result in substantial emotional, psychological, and financial costs to affected persons, their families, and society. The direct and indirect lifetime costs for cerebral palsy were recently estimated to be $445,000 (in 1988 dollars) per affected person (12). MADDSP data indicate that 1% of children 3-10 years of age in metropolitan Atlanta have a serious developmental disability and that 16% of these affected children have more than one developmental disability. Furthermore, although MADDSP includes most of the major developmental disabilities, some disabilities (e.g., autism and epilepsy) have not yet been incorporated into MADDSP. Other disabilities (e.g., learning and behavioral disabilities) are more difficult to identify and include in a surveillance system; the inclusion of such disabilities likely would substantially increase the prevalence of developmental disabilities.

The validity of the ascertainment methodology of MADDSP relies on the consequences of the Individuals with Disabilities Education Act (5). Because this law requires public schools to provide educational services to children who have developmental problems, public schools must identify and maintain information concerning such children. MADDSP has employed this requirement to assist in and enhance surveillance; however, nearly 20% of children who had cerebral palsy were identified from sources other than educational services.

Although MADDSP is an active surveillance system, its function is dependent on data collected and used for purposes other than public health surveillance. Consequently, some records do not contain the information necessary to determine a child's eligibility for MADDSP. Although few children were found to be ineligible for inclusion because of insufficient information, some eligible children may have been excluded from surveillance because they were not identified as having the disability or, even if they were identified previously, did not need continuing special care or services. These children are likely those with milder forms of the disabilities. School-age children are screened periodically for vision and hearing impairments, whereas children who have mental retardation or cerebral palsy are identified by the medical and educational systems because of their need for special care or because they cannot adapt or function successfully in their environment. Because not all school-age children are systematically evaluated for cognitive and motor deficits, some biases may increase the likelihood of identifying children who have certain demographic or socioeconomic characteristics.

The specific findings from MADDSP are consistent with findings from previous studies and expand the knowledge of the epidemiology of developmental disabilities in a large U.S. population group. Specifically, MADDSP rates for each of the disabilities among children 10 years of age concur with those of a previous CDC study of children 10 years of age that involved a more detailed ascertainment procedure (Table_10) (4) and are within the ranges reported in other studies (13-20).

With the exception of vision impairment, the prevalence of developmental disabilities among children living in the metropolitan- Atlanta area varied substantially by age, race, and sex. The prevalence of each of the disabilities increased with age because many children are not identified as having disabilities until they attend school -- a pattern that has been noted in previous studies (13,14,17,18). Rates for children 3-4 years of age were probably lower because 1991 was the first year in which public schools provided educational services to this age group. The unusual age pattern among children who had disabling cerebral palsy (i.e., an increase in prevalence up to 5 or 6 years of age and a decrease thereafter {which did not occur among children who had nondisabling cerebral palsy}) suggests an increase in mortality or out-migration among this group. Children are followed longitudinally in this surveillance program; therefore, future analyses may be able to address this observation directly.

The higher rates of mental retardation, cerebral palsy (especially nondisabling cerebral palsy), and hearing impairment for black children were also consistent with rates of previous studies (10,21-25). A substantial proportion of the difference in the reported mental retardation rates between black and white children likely reflects socioeconomic disparities (26,27); cerebral palsy and hearing impairment may also be associated with such disparities. Another factor contributing to higher rates of mental retardation among black children may be the use of standardized intelligence tests designed to test skills considered relevant to intelligence by the predominant culture (28).

These race-related differences suggest an important strategy for preventing mental retardation -- ameliorating those aspects of the socioeconomic environment that negatively influence the cognitive ability of children. Future epidemiologic studies should be designed to further the understanding of specific aspects of the social environment that may impair cognitive ability; such knowledge could then be used to target interventions to those children at greatest risk.

The slightly elevated rates of mental retardation and hearing impairment among boys -- particularly among black children -- have been reported previously (17,10,25). These discrepancies may result, in part, from both sex-linked genetic disorders and more frequent referral and testing of boys because of behavioral problems in school.

Although genetic, metabolic, and infectious factors are the cause of some cases of these developmental disabilities, the etiologies of most cases are undetermined. MADDSP enables ongoing monitoring of the occurrence of four common developmental disabilities in a community setting, which may lead to the identification of new risk factors for such disabilities. The demographic patterns described in this report may reflect social or other characteristics unique to the study population.

References

1. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives -- full report, with commentary. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991;DHHS publication no. (PHS)91-50212.

2. Crocker AC. The spectrum of medical care for developmental disabilities. In: Rubin IL, Crocker AC, eds. Developmental disabilities: delivery of medical care for children and adults. Philadelphia, PA: Lea & Febiger, 1989.

3. Yeargin-Allsopp M, Murphy CC, Oakley GP, et al. A multiple source method for studying the prevalence of developmental disabilities in children: the Metropolitan Atlanta Developmental Disabilities Study. Pediatrics 1992;89:624-30.

4. Edmonds LD, Layde PM, James LM, et al. Congenital malformations surveillance: two American systems. Int J Epidemiol 1981;10:247-52.

5. Individuals with Disabilities Education Act Admendments of 1991, PL 102-119. 20 USC 1400 et seq. Federal Register 1991;137(1901).

6. International classification of diseases, ninth edition. Manual of the international statistical classification of diseases, injuries, and causes of death. Vol. 1. Geneva: World Health Organization, 1977.

7. Mutch L, Alberman E, Hagberg B, Kodama K, Perat M. Cerebral palsy epidemiology: where are we now and where are we going? Dev Med Child Neurol 1992;34:547-55.

8. Pinto-Martin JA, Riolo S, Cnaan A, et al. Cranial ultrasound prediction of disabling and nondisabling cerebral palsy at age two in a low birth weight population. Pediatrics 1995;95:249-54.

9. Rabin I. Children with hearing impairment. In: Swaiman KF, ed. Pediatric neurology. St Louis: CV Mosby, 1989:895-908.

10. Murphy CC, Yeargin-Allsopp M, Decoufle P, Drews CD. Adminstrative prevalence of mental retardation in 10-year-old children, metropolitan Atlanta, 1985 through 1987. Am J Public Health 1995;85:319-23.

11. Kleinbaum DG, Kupper LL, Morgenstern H. Epidemiologic research: principles and quantitative methods. Belmont, CA: Lifetime Learning Publications, 1982.

12. Waitzman NJ, Romano PS, Scheffler RM. Estimates of the economic costs of birth defects. Inquiry 1994;31:188-205.

13. Kiely M. The prevalence of mental retardation. Epidemiol Rev 1987;9: 194-218.

14. Kiely M, Lubin RA, Kiely JL. Descriptive epidemiology of cerebral palsy. Public Health Rev 1984;12:79-101.

15. Elliott LL. Epidemiology of hearing impairment and other communicative disorders. Adv Neurol 1978;19:399-420.

16. Martin JA. Aetiological factors relating to childhood deafness in the European community. Audiology 1982;21:149-58.

17. Schein JD. Childhood hearing loss: epidemiology and implications. Birth Defects 1980;16:3-7.

18. Goldstein H. The reported demography and causes of blindness throughout the world. Adv Ophthalmol 1980;40:1-99.

19. Halldorsson S, Bjornsson G. Childhood blindness in Iceland: a study of legally blind and par-tially seeing children in Iceland 1978. Acta Ophthalmol 1980;58:237-42.

20. Stewart-Brown SL, Haslum MN. Partial sight and blindness in children of the 1970 birth cohort at 10-years-of-age. J Epidemiol Community Health 1988;42:17-23.

21. Reschly DJ, Jipson FJ. Ethnicity, geographic locale, age, sex, and urban-rural residence as variables in the prevalence of mild retardation. Am J Ment Defic 1976;81:154-61.

22. Murphy CC, Yeargin-Allsopp M, Decoufle P, Drews CD. Prevalence of cerebral palsy among ten-year-old children in metropolitan Atlanta, 1985 through 1987. J Pediatr 1993;123(suppl):S13-S20.

23. Torfs CP, van den Berg BJ, Oechsli FW, Cummins S. Prenatal and perinatal factors in the etiology of cerebral palsy. J Pediatr 1990; 116:615-9.

24. Haerer A, Anderson D, Schoenberg B. Prevalence of cerebral palsy in the biracial population of Copiah County, Mississippi. Dev Med Child Neurol 1984;26:195-9.

25. Drew CD, Yeargin-Allsopp M, Murphy CC, Decoufle P. Hearing impairment among 10-year-old children: metropolitan Atlanta, 1985 through 1987. Am J Public Health 1994;84:1164-6.

26. Yeargin-Allsopp M, Drews CD, Decoufle P, Murphy CC. Mild mental retardation in black and white children in metropolitan Atlanta: a case-control study. Am J Public Health 1995;85:324-8.

27. Brooks-Gunn J, Klebanov P, Duncan GJ. Ethnic differences in children's intelligence tests: role of economic deprivation, home environment, and maternal characteristics. Child Dev (in press).

28. Mercer JR. Labeling the mentally retarded. Berkeley, CA: University of California Press, 1973.

Public Law 94-142.

TABLE 1. Age-specific prevalence of mental retardation among children 3-10 years of age, by level of mental retardation --
Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
============================================================================================================================
                                Level of mental retardation *
             -----------------------------------------------------------------
                  Mild            Moderate          Severe          Profound         Total +
             --------------     ------------     ------------     ------------   --------------
Age (yrs)      No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &
-----------------------------------------------------------------------------------------------
3-4            244     3.7       36     0.5       21     0.3       30     0.5      343     5.2
5-6            295     4.7       89     1.4       65     1.0       31     0.5      483     7.6
7-8            409     6.6      110     1.8       71     1.1       28     0.5      620    10.0
9-10           499     8.2      166     2.7       59     1.0       23     0.4      747    12.3

Total        1,447     5.7      401     1.6      216     0.9      112     0.4    2,193     8.7
-----------------------------------------------------------------------------------------------
* Mild=intelligence quotient (IQ) of 50-70; moderate=IQ of 35-49; severe=IQ of 20-34; and profound=IQ of <20.
+ Includes 17 children whose level of mental retardation was unknown.
& Rate per 1,000 children.
============================================================================================================================

TABLE 2. Prevalence of mental retardation among children 3-10 years of age, by level of mental retardation, sex, and race
-- Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
===========================================================================================================================
                                        Level of mental retardation *
                     -----------------------------------------------------------------
                          Mild            Moderate          Severe          Profound        Total +
                     --------------     ------------     ------------     ------------   --------------
Sex      Race          No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &
-------------------------------------------------------------------------------------------------------
Male     White         330     4.4       94     1.3       51     0.7       22     0.3      503     6.8
         Black         538    11.3      149     3.1       78     1.6       24     0.5      791    16.6
         Total         892     6.9      255     2.0      133     1.0       48     0.4    1,335    10.4

Female   White         255     3.6       58     0.8       33     0.5       32     0.5      384     5.4
         Black         292     6.3       81     1.7       48     1.0       31     0.7      454     9.8
         Total         557     4.5      146     1.2       83     0.7       64     0.5      858     6.9

Total    White         586     4.0      152     1.0       84     0.6       54     0.4      887     6.1
         Black         829     8.8      230     2.4      126     1.3       55     0.6    1,245    13.2
         Total @     1,447     5.7      401     1.6      216     0.9      112     0.4    2,193     8.7
-------------------------------------------------------------------------------------------------------
* Mild=intelligence quotient (IQ) of 50-70; moderate=IQ of 35-49; severe=IQ of 20-34; and profound=IQ of <20.
+ Includes 17 children whose level of mental retardation was unknown.
& Rate per 1,000 children.
@ Includes 61 children of races other than white or black.
===========================================================================================================================

TABLE 3. Age-specific prevalence of cerebral palsy (CP) among children 3-10 years of
age, by severity -- Metropolitan Atlanta Developmental Disabilities Surveillance
Program, 1991
======================================================================================================
                  Severity of CP
          -------------------------------
          Nondisabling CP  Disabling CP *    Total CP +
          ---------------  --------------   ------------
Age (yrs)   No.   Rate &    No.   Rate &    No.   Rate &
--------------------------------------------------------
3-4          48     0.7      63     1.0     135     2.0
5-6          61     1.0      98     1.6     177     2.8
7-8          58     0.9      94     1.5     159     2.6
9-10         53     0.9      78     1.3     137     2.3

Total       220     0.9     333     1.3     599     2.4
--------------------------------------------------------
* Children in this category require the use of assisted devices for ambulation either intermittently
  or at all times.
+ Includes 46 children who had CP of unknown severity.
& Rate per 1,000 children.
======================================================================================================

TABLE 4. Prevalence of cerebral palsy (CP) among children 3-10 years of age, by
severity, sex, and race -- Metropolitan Atlanta Developmental Disabilities Surveil-
lance Program, 1991
======================================================================================================
                           Severity of CP
                   -------------------------------
                   Nondisabling CP  Disabling CP *    Total CP +
                   ---------------  --------------   ------------
Sex      Race        No.   Rate &    No.   Rate &    No.   Rate &
-----------------------------------------------------------------
Male     White        56     0.8      92     1.2     157     2.1
         Black        66     1.4      71     1.5     154     3.2
         Total       129     1.0     169     1.3     322     2.5

Female   White        32     0.5      89     1.3     130     1.8
         Black        55     1.2      70     1.5     138     3.0
         Total        91     0.7     164     1.3     277     2.2

Total    White        90     0.6     181     1.3     287     2.0
         Black       121     1.3     141     1.5     292     3.1
         Total @     220     0.9     333     1.3     599     2.4
-----------------------------------------------------------------
* Children in this category require the use of assisted devices for ambulation either intermittently
  or at all times.
+ Includes 46 children who had CP of unknown severity.
& Rate per 1,000 children.
@ Includes 21 children of races other than white or black.
======================================================================================================

TABLE 5. Age-specific prevalence of hearing impairment among children 3-10 years
of age, by level of impairment -- Metropolitan Atlanta Developmental Disabilities
Surveillance Program, 1991
=============================================================================================
                      Level of hearing impairment *
              ----------------------------------------------
                Moderate          Severe          Profound          Total
              ------------     ------------     ------------     ------------
Age (yrs)     No.   Rate +     No.   Rate +     No.   Rate +     No.   Rate +
-----------------------------------------------------------------------------
3-4            23     0.4       11     0.2       25     0.4       59     0.9
5-6            26     0.4       15     0.2       19     0.3       60     1.0
7-8            31     0.5       17     0.3       30     0.5       78     1.3
9-10           39     0.6       20     0.3       27     0.4       86     1.4

Total         119     0.5       63     0.3      101     0.4      283     1.1
-----------------------------------------------------------------------------
* Moderate=children who had a hearing loss of 40-64 decibles (dBs); severe=children who had
  a hearing loss of 65-84 dBs; and profound=children who had a hearing loss of >=85 dBs.
+ Rate per 1,000 children.
=============================================================================================

TABLE 6. Prevalence of hearing impairment among children 3-10 years of age, by level of impairment, sex, and race --
Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
===================================================================================================================================
                             Level of hearing impairment *
                     ----------------------------------------------
                       Moderate          Severe          Profound          Total
                     ------------     ------------     ------------     ------------
Sex      Race        No.   Rate +     No.   Rate +     No.   Rate +     No.   Rate +
------------------------------------------------------------------------------------
Male     White        32     0.4       20     0.3       27     3.6       79     1.1
         Black        32     0.7       16     0.3       26     5.5       74     1.6
         Total        70     0.5       39     0.3       57     4.4      166     1.3

Female   White        32     0.5       13     0.2       19     2.7       64     0.9
         Black        14     0.3       11     0.2       22     4.7       47     1.0
         Total        49     0.4       24     0.2       44     3.6      117     0.9

Total    White        64     0.4       33     0.2       46     3.2      143     1.0
         Black        46     0.5       27     0.3       48     5.1      121     1.3
         Total &     119     0.5       63     0.3      101     4.0      283     1.1
------------------------------------------------------------------------------------
* Moderate=children who had a hearing loss of 40-64 decibles (dBs); severe=children who had a hearing loss of 65-84 dBs; and pro-
  found=children who had a hearing loss of >=85 dBs.
+ Rate per 1,000 children.
& Includes 19 children in racial groups other than white or black.
===================================================================================================================================

TABLE 7. Age-specific prevalence of vision impairment among children 3-10 years of age, by level of impairment --
Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
====================================================================================================================================
                       Level of vision impairment *
              ----------------------------------------------
                Moderate          Severe          Profound         Total +
              ------------     ------------     ------------     ------------
Age (yrs)     No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &
-----------------------------------------------------------------------------
3-4             2    <0.1        8     0.1       11     0.2       29     0.4
5-6             5     0.1       22     0.4       14     0.2       52     0.8
7-8            20     0.3       16     0.3       23     0.4       69     1.1
9-10           13     0.2       22     0.4       16     0.3       59     1.0

Total          40     0.2       68     0.3       64     0.3      209     0.8
-----------------------------------------------------------------------------
* Moderate=children who had visual acuity (VA) of 20/70-20/160; severe=children who had VA of 20/200-20/400; and profound=children
  who had VA of >=20/500.
+ Includes 37 children whose level of vision impairment was unknown.
& Rate per 1,000 children.
====================================================================================================================================

TABLE 8. Prevalence of vision impairment among children 3-10 years of age, by level of impairment, sex, and race --
Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
====================================================================================================================================
                              Level of vision impairment *
                     ----------------------------------------------
                       Moderate          Severe          Profound         Total +
                     ------------     ------------     ------------     ------------
Sex      Race        No.   Rate &     No.   Rate &     No.   Rate &     No.   Rate &
------------------------------------------------------------------------------------
Male     White        16     0.2       26     0.4       19     0.3       70     0.9
         Black        10     0.2       13     0.3       12     0.3       42     0.9
         Total        26     0.2       42     0.3       32     0.3      117     0.9

Female   White         7     0.1       16     0.2       17     0.2       51     0.7
         Black         5     0.1       10     0.2       15     0.3       39     0.8
         Total        14     0.1       26     0.2       32     0.3       92     0.7

Total    White        23     0.2       42     0.3       36     0.3      121     0.8
         Black        15     0.2       23     0.2       27     0.3       81     0.9
         Total @      40     0.2       68     0.3       64     0.3      209     0.8
------------------------------------------------------------------------------------
* Moderate=children who had visual acuity (VA) of 20/70-20/160; severe=children who had VA of 20/200-20/400; and profound=children
  who had VA of >=20/500.
+ Includes 37 children whose level of vision impairment was unknown.
& Rate per 1,000 children.
@ Includes seven vision-impaired children in racial groups other than white or black.
====================================================================================================================================

TABLE 9. Number and percentage of disabled children 3-10 years of age who had coexisting developmental disabilities, by
type of disability -- Metropolitan Atlanta Developmental Disabilities Surveillance Program, 1991
==========================================================================================================================================
                                                             Type of coexisting disability
                                 -------------------------------------------------------------------------------------
                                 Any coexisting
                                 developmental         Mental           Cerebral          Hearing            Vision
                                  disability *      retardation          palsy           impairment        impairment
Type of               No. of     --------------     ------------      ------------      ------------      ------------
disability           children     No.     (%)       No.     (%)       No.     (%)       No.      (%)      No.     (%)
----------------------------------------------------------------------------------------------------------------------
Mental retardation     2,193      473     (22)       --       --      381     (17)       58      (3)      145     ( 7)

Cerebral palsy           599      396     (66)      381     (64)       --       --       22      (4)      101     (17)

Hearing
  impairment             283       66     (23)       58     (20)       22     ( 8)       --       --        6     ( 2)

Vision impairment        209      152     (73)      145     (69)      101     (48)        6      (3)       --       --
----------------------------------------------------------------------------------------------------------------------
* The numbers in this column are less than the sum of the four types of disabilities because some children had more than one additional
  disability.
==========================================================================================================================================

TABLE 10. Prevalence of selected developmental disabilities obtained from the
Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP)
and other previous studies, by type of disability
=================================================================================================
                                     Previous CDC     Other previous
                       MADDSP *+       study (3)      studies (11-18)
                       ---------     ------------     ---------------
Type of disability       Rate &         Rate &            Rate &
---------------------------------------------------------------------
Mental retardation        11.6           12.0            3.1-43.6
Cerebral palsy             2.3            2.3            2.0- 3.0
Hearing impairment         1.5            1.1            0.8- 2.0
Vision impairment          0.6            0.7            0.3- 0.6
---------------------------------------------------------------------
* Limited to children 10 years of age.
+ For comparability, only children who had corrected visual acuity of >=20/200 were included in
  rate calculations.
& Rate per 1,000 children.
=================================================================================================

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