Detecting Age Prone to Growth Retardation in Children Through a Bi-Response Nonparametric Regression Model with a Penalized Spline Estimator.

Background: The growth of children aged 0-60 months can impact their subsequent growth and development. This study aims to identify the vulnerable age for boys and girls, who experience growth retardation within this age range. Methods: The study design used was a cross-sectional approach in which each child's measurement data was only taken once. The data were obtained from weighing results at the Health Integrated Service Post in South Sulawesi Province in 2022. The number of data analyzed was 698 children, namely 369 boys and 329 girls by considering the factors of age, weight, and height. We used a nonparametric bi-response regression model estimated using a penalized spline. The knots used are 12, 24, 36, and 48 on each model. Results: The value of the penalized spline regression coefficient in the model indicates that the child's growth is slowed down and is not within normal limits. This can be seen in the weight and height of boys from the age of reaching 12 months to 24 months, only increasing by about 0.3 kg and 0.3 cm. For girls, the problem occurs from the age of 24 to 36 months, namely their weight increases by about 0.6 kg, and their height increases by about 1 cm. Conclusions: The analysis results show that boys' growth slows down at 2 years of age and continues until 5 years of age. In the case of girls, their growth begins to slow when they are 3 years old until they reach 5 years old.