In ancient times, attributing effects to the moon made some sense. If it could change tides, which everyone except Galileo recognized it did, why not cause effects in people?
Today, we know better, and yet beliefs persist. The reason is confirmation bias, which makes conservatives and liberals believe they are smarter than their opposition and which results in a lot of correlation-causation papers, in everything from psychology to epidemiology. Even in biology. Epigenetics is the modern day life sciences equivalent of 'it must be a full moon'.
So perhaps nurses notice more people getting hurt in crazy stunts during a full moon but it isn't really the case. Instead, confirmation bias makes people think the moon is the culprit, the same way some people believe there are more earthquakes now or that gluten-free food makes them feel better. The moon did not go back in time and get women pregnant and it lacks the gravity to cause more births when it is closer or fuller, yet some people truly still think it matters, whereas most just say things like "it must be a full moon" in jest. A 2004 study in a nursing journal nonetheless suggested that the full moon influenced the number of hospital admissions in a medical unit in Barcelona.
Jean-Luc Margot, a UCLA professor of planetary astronomy, writes in Nursing Research that there is no lunar influence on automobile accidents, hospital admissions, surgery outcomes, cancer survival rates, menstruation, births, birth complications, depression, violent behavior or criminal activity, Margot writes.
Still, it is unlikely to go away. People tend to interpret information in a way that confirms their beliefs and ignore data that contradict them. When life is hectic on the day of a full moon, many people remember the association because it confirms their belief. But hectic days that do not correspond with a full moon are promptly ignored and forgotten because they do not reinforce the belief.
It isn't just more weird behavior in emergency rooms, obviously confirmation bias can have more deadly effect, like when residents of California and Oregon set off a chain of anti-science hysteria about vaccines, something that was once only the domain of fringe religious fundamentalists.
But rich elites are not going to change their minds about all science any time soon.
"Perhaps we can start by correcting our delusions about the moon, and work from there," says Margot.
