SuperImposition by Translation And Rotation (SITAR) is the most beautiful non-linear modelling technique known to man, applied here to show preterm girls treated with antenatal steroids grew on average 2.8cm taller than those without, after controlling for gestational age and parental height:

Spline modelling is essential to appreciate non linear relationships, and changepoint analysis can add insights into relationships that you think may be linear on the log scale. Let's keep analysis explainable: Pictures can paint a thousand words! authors.elsevier.com/sd/article/S...