Adapting the Bayley Scales of infant and toddler development in Ethiopia: evaluation of reliability and validity.

Children were only assessed at 30 and 42 months, so the study does not show that the adapted scale works across the full 1 to 42 month age range. The reliability sample was a convenience sample of children aged 2 to 3 years, not a random sample. The validation sample was chosen because birthweight was measured within 48 hours of birth. Children whose mothers lacked this measurement were more likely to be non-literate and first-time mothers. Several items were flagged as content-validity problems, especially colour, pronoun, plural and scissors-based tasks, so low scores on those items may reflect unfamiliarity rather than delay. The gross motor scale lost items because stairs were not available, and its consistency was weaker at 42 months. The study reports reliability and validity evidence, not a test of whether the adapted scale diagnoses developmental delay.

The authors reported no conflicts of interest. The study was part of the C-MaMiE project, which covered healthcare costs for participating mothers and children.

Do not read this as proof that the adapted Bayley Scales diagnose developmental delay in all low-income settings. The study was done in rural Ethiopia, only at 30 and 42 months, and several items were not valid, so a low score on one item may reflect unfamiliarity with the task rather than a child's ability.