Table 1.

Comparison of cognitive level, IQ, mental age, Piagetian stage, and communication skills in patients with cognitive disabilities

COGNITIVE LEVEL	IQ	MENTAL AGE, Y	PIAGETIAN STAGE	COMMUNICATION SKILLS
Borderline	70 to 84	12 to 16	Formal operations	Read and write at a grade 2 to 8 level
Mild	55 to 69	8 to 12	Concrete operations to formal operations	Read and write simple phrases, ability to follow simple instructions using prepositions
Moderate	43 to 54	5 to 8	Preoperational to concrete operations	Minimal sight vocabulary, understands 2-step commands
Severe	Hard to test	2 to 5	Preoperational	Telegraphic speech, understands 1-step commands
Profound	Hard to test	Infancy to 2	Sensorimotor	Orients to speech, small vocabulary

Adapted from Lougheed.⁴