Nancy Bayley

Nancy Bayley (28 September 1899 – 25 November 1994) was an American psychologist best known for her work on the Berkeley Growth Study and the subsequent Bayley Scales of Infant Development. Originally interested in teaching, she eventually gained interest in psychology, for which she went on to obtain her Ph.D. in from the University of Iowa in 1926. Within two years, Bayley had accepted a position at the Institute for Child Welfare (now called the Institute for Human Development) at the University of California, Berkeley. There she began the longitudinal Berkeley Growth Study, which worked to create a guide of physical and behavioral growth across development. Bayley also examined the development of cognitive and motor functions in children, leading to her belief that intelligence evolves over the course of child development. Until the age of 8, Bayley was a sickly child and could not attend school. The study aimed to study human development from infancy to adulthood on a range of physical, psychological, and physiological characteristics. The purpose of the BSID-III is to gain further information about a child's developmental milestones and abilities, as well as to intervene at an early age if a learning disability presents itself.

Measurements The Mental and Motor Scales have remained relatively the same through all versions, with some changes made to the Behavior Rating Scale. These changes include: age range, norms altered to function more successfully with modernization, and greater validity and reliability. The Mental Scale presented in BSID-II assesses children using a normalized standardized scoring system – the Mental Development Index (MDI) – and a standard scoring system – the Psychomotor Development Index (PDI). The MDI is used to measure mental capabilities in children, including sensory and perceptual acuities, object constancy, memory, learning, problem solving, early verbal communication, early abstract thinking ability, and early number concepts. The PDI is used to gauge control of the body, such as fine and gross motor skills. The Behavior Rating Scale presents a numerical assessment of a child's attention, arousal, orientation/engagement, emotional regulation, and motor ability. The BSID-III is most beneficial for studies regarding developmental, psychological, and neuropsychological information in children up to 42 months old; after 42 months of age the information becomes less reliable. The amount of time required to administer the test depends greatly on the age of the child. This variability occurs because each portion of the test has specific instructions on how to administer it to the child. For instance, in the motor tasks there are certain positions the child is to be placed in. When scoring the test, each task throughout both motor and cognitive is either given or not given credit based on how the child responds to the task that is presented. Notes are made along the way while administering the test if there are refusals made, items are omitted, or there is an issue with the caregiver report. In these cases, an examiner will go back and administer another exam to obtain data for that test.

Selected works Bayley, N., & Jones, H. E. (1937). Environmental correlates of mental and motor development: A cumulative study from infancy to six years. Child Development, 8, 329–341.

Bayley, N. (1940). Studies in the development of young children. Berkeley: University of California Press

Jones, H. E., & Bayley, N. (1941). The Berkeley growth study. Child Development, 12(2), 167–173.

Bayley, N. (1949). Consistency and variability in the growth of intelligence from birth to eighteen years. Journal of Genetic Psychology, 75, 165–196.

Bayley, N. (1966). Bayley Scales of Infant Development. New York: Psychological Corporation.

Bayley, N. (1968). Behavioral correlates of mental growth: Birth to thirty-six years. American Psychologist, 23, 1–17.