Too much covariates in a multivariable model may cause the problem of overfitting

Many thanks for the thoughtful insights into our work by Prof. Zhang and coworkers. We strongly agree with the reader that red blood cell distribution width (RDW) can be influenced by varieties of medical conditions including but not limited to anemia, renal dysfunction, hepatic dysfunction, thyroid disease, transfusion, acute or chronic inflammation, neurohumoral activation, malnutrition (i.e., iron, vitamin B12 and folic acid), ethnicity, bone marrow depression, and use of some medications (1-4).