The following quote is from the paper Evaluation of the Accuracy of Different Methods Used to Estimate

Question:

The following quote is from the paper €œEvaluation of the Accuracy of Different Methods Used to Estimate Weights in the Pediatric Population€ (Pediatrics [2009]: e1045€“e1051): As expected, the model demonstrated that weight increased with age, but visual inspection of an age versus weight plot demonstrated a nonlinear relationship unless infants and children were analyzed separately. The linear coefficient for age as a predictor of weight was 6.93 in infants and 3.1 to 3.48 in children. This quote suggests that when a scatterplot of weight versus age was constructed for all 1011 children in the study described in the paper, the relationship between y = weight and x = age was not linear. When the 1011 children were separated into two groups€”infants (age birth to 1 year) and children (age 1 to 10 years)€”and separate scatterplots were constructed, the relationship between weight and age appeared linear in each scatterplot. The slopes reported in the given quote (referred to as €œthe linear coefficient€) are expressed in kg/year. Briefly explain why the relationship between weight and age in the scatterplot for the combined group would appear nonlinear.