Are there really more births on full moons?

If you ask around, you'll probably find that most people who believe in the lunar effect on birth rates rely on anecdotal proof: namely, stories related by medical professionals working in the obstetrics field. Labor nurses are often cited as providing evidence of the effect in the form of personal experience, basically relating that the number of labor-ward admissions increases on a full moon.

And who doesn't trust a labor nurse? Certainly, they're experts in the area of childbirth. But for a number of reasons that we'll get into on the next page, anecdotal evidence of this sort is notoriously unreliable.

There is, however, a limited body of more empirical evidence for the existence of the phenomenon. A 1959 study broke the month into consecutive three-day periods and found that the three days of a "full moon window" -- the day before, day of and day after a full moon -- had more births than any other single three-day period [source: Shulman]. Another study, this one published in 1966, studied birth rates by moon phase -- full, half, one-quarter and three-quarter. The authors found that within the study period, more births centered around the full-moon phase than any other [source: Shulman].

But as you get deeper into the scientific study of the connection between birth and the full moon, it quickly becomes clear that these studies supporting the lunar effect are an anomaly. The vast majority of evidence reveals the lunar effect to be myth, not scientific reality.

And sometimes, studies seem to be misread by supporters of the belief. An article on the Web site BirthSource, for instance, makes the following statement:

However, if you look at the abstract for the study the text refers to, [please note, in the source list, the article cites the study as reference "5," but in fact this text refers to reference "3."] you find the following statement:

So, where does that leave us?

Anecdotal and anomalous statistical evidence aside, it's tough to find proof that more babies are born on a full moon. The topic has been studied pretty extensively, though, and it's very easy to find evidence disproving the connection.

Here are just a handful of the scientific studies that have found no connection between the full moon and birth rates:

1957: Looked at a series of days with abnormally high numbers of births and tried to correlate them with full moons. No correlation was found [source: Shulman].

1987: Looked at U.S. birth rates by decade and found no correlation between full moons, birth rates or conception rates [source: Shulman].

1996: Looked at 100 previous studies on lunar effects and found no statistically significant proof of the moon's effect on birth, violence, suicides, major disasters or a dozen other supposedly lunar-connected phenomena [source: Skeptic's Dictionary].

1998: Looked at 3,706 births and found that "scientific analysis of data does not support the belief that the number of births increases as the full moon approaches, therefore it is a myth not reality" [source: ScienceDirect].

2005: Looked at 564,039 births in North Carolina between 1997 and 2001 and found "no predictable influence of the lunar cycle on deliveries or complications" [source: PubMed].

2006: Looked at births over a 28-year period in Australia and found that "full moons are not associated with any significant change in the number of conceptions, births, or deaths" [source: Gans].

If there's so much evidence against the lunar effect, why is the belief so widespread? For pretty much the same reasons why lots of other old wives' tales or urban legends pick up a strong following: It's easy to believe.

The belief that the number of births increases on a full moon is a longstanding one, and one with cultural roots. Folkloric tales have, by definition, been around for long enough to seem like common sense. It can be counterintuitive to argue with a belief that has been passed down through countless generations.

It can also be hard to argue with experts like labor nurses and paramedics. Who would know better?

And then there's the media's love of the spooky old full moon. The press loves a good human interest story about the full moon filling up labor wards or causing a paramedic shortage; and Hollywood loves the iconic werewolf-howling-at-the-full-moon image.

Cognitive bias plays a strong role, as well. Cognitive bias is a psychological phenomenon in which people absorb all evidence that supports their belief and ignore all evidence to the contrary. In this case, that could mean a nurse noticing every time the ward is full on a full moon, but not noticing every time it's empty on a full moon.

And finally, there are some simple misconceptions regarding certain aspects of the moon. For instance, a full moon really only lasts an instant; a "full moon window" of three days, or even one day, is an artificial construct [source: Shulman]. Also, many people believe the moon's gravity is extremely powerful, since it affects the tides; in fact, it's a relatively weak gravitational force, and one unlikely to have an effect on the human body [source: Skeptic's Dictionary]. And the gravitational force that effects the tides is not even phase-related; it's a function of how far the moon is from Earth at any given time, which is different from the phase the moon is in [source: Skeptic's Dictionary].

But hey, all is not lost. We can still hang on to one of the best lunar-effect beliefs: There's no hard evidence that the moon doesn't affect werewolves.

For more information on the lunar effect and related topics, look over the links on the next page.