A Comparison Study of the norms of Tehran and Iran in the Performance of 1-42-month-old children on the Bayley Scale

There is a wide variety of sociocultural and environmental background characteristics in different geographical places of Iran. The aim of this study was to investigate the rates of developmental delay in Tehran in comparison to the norm of Iran, using the Bayley III measure.

This cross sectional study was a part of a national study conducted in Iran, between 2014 and 2016. During the study period, five hundred fifty Persian speaking children in Tehran were included. The sampling was in proportion to the population of children covered in each region. First, the differences between the scaled scores, based on the norms of Tehran and Iran were calculated and then, a one sample Multivariate Analysis of Variance (MANOVA) was used, which showed a significant difference between the scaled scores. Next, we used a univariate analysis to find which scales these significant differences were generated from. Finally, the rate of children with low scores (<-1SD, and <-2 SD) were compared by means of the McNemar analyses.

The numbers of male participants were 310 (54.5%). The mothers in the sample of Tehran had higher educational levels in comparison to those in the sample of Iran (P= 0.001). Considering Iran’s norm compared to Tehran’s norm leads to significantly fewer rates of delay, on cognition scale (<-1SD; 11.6% to 19.8%) and fine motor scale (<-1SD; 15.1% to 21.1%)(<-2SD; 1.6% to 3.3%) respectively (p <0.01). The differences in estimation rate were somewhat age-dependent. The greatest difference between the norm of Tehran and Iran was in the age group of “25 months 16 days to 42 months 15 days”.

In some developmental domains, the norm of Iran in comparison to that of Tehran indicates a lower rate of children with developmental delay.