>"Can't we just look at the actual rate of death from brain cancer (death rates not diagnosis rates since this reduces the bias from changes in how often it is

>"Can't we just look at the actual rate of death from brain cancer (death rates not diagnosis rates since this reduces the bias from changes in how often it is detected), and see if there's been an increase in brain cancer?" Just seeing an increase could be due to anything, the prediction "if cell phones could cause cancer then there would be an increase" is too vague. Instead someone needs to come up with a mathematical model that predicts a precise pattern of cancer due to a precise exposure schedule. Then that model would need to be verified later on new data. That type of "testing a precise prediction against real world observational data" study is actually the gold standard of science (eg, astronomy). You need to do the hard work of coming up with the precise model though, and people attracted to medicine generally dont like math.