1). Why was the Cox regression used?

2) How did the authors check the assumption of proportional hazard?

3). What was the prognostic value of BNP and NT-proBNP? Do not refer to the ROC curves.

Use the article below to answer the questions.

Link: https://pubmed.ncbi.nlm.nih.gov/16777915/ [copy and paste is needed in order to work]

Reference: Masson S, Latini R, Anand IS, Vago T, Angelici L, Barlera S, Missov ED, Clerico A, Tognoni G, Cohn JN; Val-HeFT Investigators. Direct comparison of B-type natriuretic peptide (BNP) and amino-terminal proBNP in a large population of patients with chronic and symptomatic heart failure: the Valsartan Heart Failure (Val-HeFT) data. Clin Chem. 2006 Aug;52(8):1528-38. doi: 10.1373/clinchem.2006.069575. Epub 2006 Jun 15. PMID: 16777915.