Despite the Bayley Scales of Infant Development second edition (BSID-II) are wide used both clinically and in research settings, only a few published studies have been examined their stability over time.
Aim of study: The aim of this study was to examine the stability of mental and motor BSID-II scores over the first three years of life.
Material and methods: All children included in this study were a sample followed up in a study on the susceptibility of the fetus and child to environmental factors. The cohort recruited prenatally in Krakow Poland, included 408 children. The mental and motor scales of BSID-II were administered to infants at the end of 12th, 24th and 36th month of life. Stability of the test scores from first to second and third assessment was evaluated using the Pearson's correlation coefficient calculated for the entire group of infants, and for the each gender separately.
Results: The older infants obtained the better outcomes in BSID-II. The correlation between the first and second assessments for the Psychomotor Developmental Index (PDI) was r = 0.30, for the Mental Developmental Index (MDI) was r = 0.33, and between the second and third assessments the correlation for the PDI was r = 0.40, for the MDI was r = 0.59. That results suggest a low or moderate degree of relationship between the tests outcomes. Only 8,8% to 34,8% of variance in the infants later BSID-II scores could be explained by their earlier scores. The correlation between the tests scores was higher between outcomes obtained by girls than boys.
Conclusion: The BSID-II should not be treated as a useful measure for predictive purposes of infants development.