Pediatric Physical Therapy has published research on the relationship between the ability to sit upright and developmental delay. Sixty five infants were evaluated when the babies were learning to sit. The amount and variability of the center of pressure (COP) of sitting was measured and data was collected. After data analysis, the results indicated that the variability of the center of pressure when learning to sit could "discriminate between infants with developmental delay and cerebral palsy". The researchers concluded that the center of pressure is an objective tool to be used to help to identify sitting postures and motor delays.
Reference: Kyvelidou, Anastasia; Harbourne, Regina T.; Stergiou, Nicholas. Severity and Characteristics of Developmental Delay Can Be Assessed Using Variability Measures of Sitting Posture Pediatric Physical Therapy. 22(3):259-266, Fall 2010. doi: 10.1097/PEP.0b013e3181ea75f1