For discussion of the survey's formal definitions of "problem" and "limited," see LAPLAYAM (Limited in kind or amount of play).

The Field Representative's Manual for 1997-2000 defined Special Education as follows:

The Manual for 1997-2000 defined Early Intervention Services as follows:

The Manuals for 2001-2018 included similarly worded definitions for Special Education and Early Intervention Services.

Two other questions gauged activity limitation in children under age 5. LAPLAYAM indicates whether young children were limited in the amount of play activities they could do because of a physical, mental, or emotional problem. For those with an affirmative response in this variable, LAPLAYAL indicates whether the child was "able to take part at all in the usual kinds of play activities" done by most children of the same age.
In 1994 and 1995, this variable is part of the Disability Supplement (NHIS-D) that collects information on disability. NHIS-D included two household interviews: in Phase I all members of sample families were screened for any indication of disability; in Phase II persons with any indication of disability were followed-up for additional information. Phase I includes sensory, communication, and mobility problems; health conditions; activities of daily living and independent activities of daily living; functional limitations; mental health; services and benefits; special health needs of children; early child development; education; relationship to respondent; and perceived disability. Phase II includes four Disability Followback Survey (DFS) questionnaires: one for children, one for adults, one for elderly persons (69 years of age and over) without any indication of disability (also called the Supplement on Aging or SOA; only in 1994), and one for persons with a history of polio.