They found that between 1995 and 2015, adult residents of Staten Island suffered from certain cancers at slightly or moderately higher rates than residents in other boroughs
The article does not make it clear therefore I am not sure why the study was only conducted from 1995 through 2015 because, the Staten Island landfill opened up in 1948 and closed in 2001 making it open for only 53 years. It would make more sense If they conducted the study earlier or compared it to those who have lived near Fresh Kills somewhat close to 1948; but they probably conducted the study in 1995 due to the increase in cancer cases.