Write down the Cox proportional-hazards model. What does the term proportional hazards mean?

Pulmonary Disease

A study was performed among 169,871 Chinese men and women in 1991 ages 40 years and older [13]. Baseline data were collected in 1991, and a follow-up exam was conducted in 1999−2000. One component of the follow-up exam was a mortality follow-up for subjects who died between 1991 and 1999, where the date and cause of death were determined from Chinese vital statistics data. Of particular interest were risk factors for death from chronic-obstructive pulmonary disease (COPD), A Cox proportional-hazards regression model was used to relate risk factors in 1991 to time of death from COPD between 1991 and 1999−2000.