Univariate linear regression models by age group. Thoracic Cobb angle, Thoracolumbar Cobb angle and Lumbar Cobb angle are the dependent variables. Rib-index (thoracic deformity) is the independent variable. The only linear association was the one between Thoracic Cobb Angle and rib-index in the age group of 14-18 years. (Predicted Thoracic Cobb Angle = -6.357 + 7.974 × (Rib-Index).