BERKELEY GROWTH STUDY

BERKELEY GROWTH STUDY

Date(s): Initiated 1928; Primary Longitudinal Data Collection 1928–1980s; Follow-ups Ongoing

Institutional Affiliation(s): Institute of Human Development (IHD), University of California, Berkeley

1. Summary

The Berkeley Growth Study (BGS) stands as one of the most seminal and long-running investigations into human development, establishing the foundation for modern longitudinal research methodology. Initiated in 1928 at the University of California, Berkeley, the primary goal of the study was to systematically chart the physical, intellectual, and personality development of a carefully selected cohort from infancy through middle and later adulthood. Unlike previous cross-sectional studies that provided only snapshots of different age groups, the BGS offered a dynamic, continuous record of individual developmental trajectories.

The study was famously led initially by psychologists Nancy Bayley and Harold Jones, who sought to empirically understand the stability and variability of mental abilities during early childhood—a topic about which little reliable longitudinal data existed at the time. The initial findings, published prominently in 1941, demonstrated the challenges of predicting adult intelligence solely based on infant measures, highlighting the complexity and fluidity of early development. The longevity and depth of the BGS data make it an indispensable reference point, particularly in the fields of developmental psychology and lifespan studies.

The sheer duration of the data collection, spanning over fifty years of continuous assessment for the original cohort, provided unprecedented insights into the interplay between genetic factors, environmental influences, and developmental milestones. The BGS, alongside the companion Berkeley Guidance Study (BGS), became central to the Institute of Child Welfare (later the IHD) at UC Berkeley, solidifying the institution’s reputation as a world leader in psychological research focusing on the entire human life course.

2. Background and Causes

The BGS originated during a period in the late 1920s when American psychology was rapidly professionalizing and shifting towards empirical, quantitative methods. There was a burgeoning interest in child welfare and development, largely spurred by the establishment of research centers funded by organizations like the Laura Spelman Rockefeller Memorial. The Institute of Child Welfare at Berkeley, founded in 1927, was one such center designed to facilitate systematic, long-term studies of children.

The primary motivation for the BGS was methodological necessity. Researchers understood that cross-sectional data—comparing 5-year-olds today with different 10-year-olds—could not capture true intra-individual change or developmental stability. Psychologists like Nancy Bayley recognized the critical need for a prospective design where the same individuals were followed over time. This approach was essential for addressing key theoretical questions, such as the relationship between early motor skills and later cognitive function, or the stability of temperament across developmental stages.

Furthermore, the early decades of the 20th century saw the widespread adoption of standardized intelligence testing. However, the validity of applying these tests to infants and the long-term predictive power of these scores remained highly controversial. The BGS was explicitly designed to generate the necessary empirical data to validate or reject the assumption that mental abilities measured in infancy were highly correlated with those measured in adulthood, driving the creation of refined measurement tools necessary for infant assessment.

3. Key Developments and Timeline

The Berkeley Growth Study followed a rigorous, multi-faceted assessment schedule that evolved as the cohort aged and research priorities shifted.

• 1928–1929: Initial Cohort Selection. The study began by enrolling 74 healthy infants born in Berkeley, California, establishing a representative cohort for normative development tracking.
• Infancy and Early Childhood (1929–1935): Data collection was intensive, sometimes occurring monthly. The focus was heavily weighted toward physical growth (height, weight, skeletal maturity), motor development, and the newly developed assessments of mental abilities. This period was critical for Nancy Bayley’s refinement of the scales that would eventually become the widely used Bayley Scales of Infant Development (BSID).
• Adolescence and Early Adulthood (1936–1950s): The focus broadened under Harold Jones to include personality dynamics, social adjustment, and physiological changes accompanying puberty. Researchers tracked educational attainment, vocational choices, and marital status, providing data on psychosocial development across major life transitions.
• 1941: Major Publication. Harold Jones and Nancy Bayley published the seminal work, The California Adolescent Study, which synthesized the initial findings on mental and physical growth, firmly establishing the BGS data in the academic literature.
• Middle and Later Adulthood (1960s–Present): As the participants entered their senior years, the study transitioned to examining health outcomes, cognitive decline, retirement adjustments, and the stability of personality traits, thus transforming into a true lifespan study. The data became invaluable for gerontological research.

4. Key Figures and Methodological Influence

The success and enduring legacy of the BGS are inextricably linked to its principal investigators, who were pioneers in developmental science.

• Nancy Bayley (1899–1994): A central figure in the BGS, Bayley’s primary contribution was the development and standardization of tools for measuring infant intelligence and development. Her meticulous work in the early phases of the study demonstrated that typical intelligence tests were often inadequate for assessing very young children, leading to the creation of instruments that measured behavioral milestones and developmental quotients rather than pure IQ. The reliability of her scales transformed clinical and research practices globally.
• Harold Jones (1894–1960): As the director of the Institute of Child Welfare and a lead investigator, Jones focused heavily on the physical aspects of growth and adolescent development. His work emphasized the relationship between physical maturity rates, emotional stability, and intellectual performance during the teenage years. He ensured the BGS maintained a strong bio-developmental perspective, integrating data on skeletal age and physiological changes with behavioral data.
• Jean Walker Macfarlane (1894–1989): While primarily known for leading the companion Berkeley Guidance Study (BGS), Macfarlane’s work often overlapped and complemented the Growth Study, providing rich clinical and personality data. The combined efforts of these three researchers created a synergistic research environment that allowed for deep, multi-dimensional analysis of individual development.

Methodologically, the BGS perfected the art of the longitudinal study. Its rigor in tracking participants, managing vast amounts of heterogeneous data (ranging from x-rays and physiological measures to behavioral observations and test scores), and developing statistical techniques to handle attrition and repeated measures set the standard for subsequent lifespan research projects around the world.

5. Consequences and Impact

The Berkeley Growth Study yielded several profound findings that fundamentally reshaped developmental psychology and assessment practices.

Perhaps the most significant consequence was the finding concerning the instability of infant intelligence measures. BGS data demonstrated that mental test scores gathered during the first two years of life showed very poor correlation with IQ scores measured during late childhood or adulthood. This counterintuitive finding challenged the prevailing notion that intelligence was a fixed, innate trait discernible immediately after birth. Instead, the study highlighted the importance of environmental stimulation and the dynamic nature of intellectual growth during the preschool years.

The BGS provided definitive normative data on physical growth, establishing curves and standards for height, weight, and skeletal maturation that were widely used in pediatrics and public health. Furthermore, the longitudinal tracking of personality traits provided crucial evidence for the moderate stability of temperament and personality across the lifespan, especially after early childhood, contributing significantly to trait theories of personality.

Finally, the study’s longevity provided invaluable insight into the effects of historical and socio-economic changes on development, as the participants lived through the Great Depression, World War II, and subsequent decades of major social transformation. The BGS remains an unparalleled resource for researchers examining aging, health psychology, and the long-term impact of early life experiences.

Further Reading

• Berkeley Growth Study (Wikipedia Entry)
• University of California, Berkeley Institute of Human Development (IHD)
• Jones, H. E., & Bayley, N. (1941). The Berkeley Growth Study. Child Development.
• Nancy Bayley Biography (American Psychological Association)