For many years, it has been accepted that a person's IQ is not sufficient to establish his or her level of functional intelligence. Rather, functional intelligence is a combination of IQ and adaptive behavior, that is, the person's ability to function successfully in the community. Most federal and state assistance programs, as well as most educational assistance programs, require that a person's Full Scale IQ be below a standard (usually 70) and that the level of adaptive behavior be consistent with expected levels for the IQ in order for the person to be classified as mentally handicapped.
Functional intelligence generally is defined as one's ability to behave adaptively in daily life. Specifically, it includes the person's ability to express and comprehend language, behave appropriately in interpersonal situations, understand and use social behaviors, protect him/herself , and care for him/herself, in terms of personal hygiene and domestic independence. It is quite possible for a person to obtain a rather low IQ, but exhibit self-maintenance and personal care skills that are substantially greater than the IQ would predict. Thus, while these persons would be classified as mentally handicapped according to the IQ alone, their adaptive performance would preclude their classification as mentally handicapped.
Although several scales and observation systems for measuring adaptive behavior have been developed since the 1940s, when the construct of adaptive behavior was formally introduced, one of the most widely accepted scales is the Vineland Adaptive Behavior Rating Scales. The VABS is used primarily with children and adolescents from birth to age 18 years, but may be used adults suspected of having a mental handicap based on obtained IQ. The scale measures adaptive behavior in four major domains, Communication, Daily Living Skills, Socialization, and Gross Motor Skills. The first three of these domains include several subdomains, as follows:
Communication Receptive Communication, Expressive Communication, Written Communication
Daily Living Skills Domestic Skills, Personal Skills, Community Skills
Socialization Interpersonal Relationships, Play/Leisure, Coping Skills
The Gross Motor Skills Domain is measured with children to age five years and with older children and adults suspected of deficiencies in this area. Also, the VABS includes a Maladaptive Behavior Scale, for use in identifying the presence of behavior problems in children thought age 18.
The VABS includes a number of items (critical behaviors) in each Subdomain, arranged by age at which the behaviors were present in the original norm group. However, the scale is administered as a semistructured interview to an informant who knows the child well (there are separate forms for parents and teachers). The interviewer asks general questions pertaining to the child's functioning in each subdomain and uses the responses to rate the examinee on each critical behavior item (2: always present, 1: sometimes present, 0: seldom or never present). Typical interviews require approximately one hour. Raw scores are converted to IQ-type standard scores (mean: 100 sd: 15) for each domain and for the composite adaptive behavior score. Score ranges are as follows: 70-80 borderline adaptive functioning; 51-55 -70: mildly deficient adaptive functioning ; 35-50: moderately deficient adaptive behavior; 20-35: severely deficient adaptive behavior; less than 20: markedly or profoundly deficient adaptive behavior. Scores above 80 are classified in approximately the same ranges (low average, average, above average, superior) as IQ scores. The Adaptive Behavior Composite score is most useful in making decisions as to whether or not the examinee's adaptive functioning is consistent with Full Scale IQ. Subdomain raw scores are intepreted according to tabled values as high, moderately high, moderately low, and low.