An article in the New York Times, published September 29, 2008, and titled "Study Finds Association between Hepatitis B and Pancreatic Cancer," reported that, for the first time, a study showed that people with pancreatic cancer are more likely than those without the disease to have been infected with the hepatitis B virus. The study, which was subsequently published in the Journal of Clinical Oncology, compared 476 people who had pancreatic cancer with 879 healthy control subjects. All were tested to see whether they had ever been infected with the viruses that cause hepatitis B or hepatitis C. The results were that no connection was found to hepatitis C, but the cancer patients were twice as likely as the healthy ones to have had hepatitis B. The researchers noted, however, that ". . .while the study showed an association, it did not prove cause and effect. More work is needed to determine whether the virus really can cause pancreatic cancer." Explain the validity of the statement in quotes.