Institute:Office of National Coordinator (ONC) Workforce Training Curriculum
Component:The Culture of Health Care
Lecture:Phrasing the clinical question
Harm and prognosis
Slide content:Evidence and Its Limits Continued 2 Case-control study continued Problem is when controls create spurious association, e.g., Coffee drinking associated with miscarriages 2016 NIH article says yes, Slate magazine article disputes findings pancreatic cancer ( MacMahon et al., 1981), but controls were patients with other GI diseases whose symptoms were exacerbated by coffee (so they drank less) Differences were not present when other appropriate controls were used (Zheng et al., 1993) 9
Slide notes:9 One of the problems with case-control studies is that they can create spurious [ spyoo r - ee -uh s] associations. A case in point was a study that purported to detect a linkage between coffee consumption and pancreatic cancer. This study was published in the New England Journal of Medicine , so it carried the prestige of that journal. It turns out that those who ran the study used the wrong control group, which shows you that sometimes even in the best of journals, bad science can get through. They used people who had other gastrointestinal diseases as the control participants. Many gastrointestinal diseases have symptoms that are exacerbated by coffee, particularly gastroesophageal [ gas - troh - ih - soff -uh- jee - uhl ] reflux. People with these other diseases drink less coffee. So, when you use them as a control group of cases versus those with pancreatic cancer, the people with pancreatic cancer drink more coffee, but the coffee is not the cause of their cancer. They drink more coffee because they can tolerate it better. In fact, when this study was repeated with an appropriate control group over a decade later, that association was disproven, and those of us who drink coffee can rest assured that we arent causing pancreatic cancer in ourselves.