Today is Friday the 13th, a day many people believe to be a day of bad luck. The fear of Friday the 13th is called paraskevidekatriaphobia, a mash up of the (mostly Greek) words "fear," "13" and "friday." 

According to Dr. Donald Dossey, a psychotherapist specializing in the treatment of phobias (who also coined the term paraskevidekatriaphobia, sometimes spelled paraskavedekatriaphobia), the figure may be as high as 21 million Americans who believe the day to be unlucky.

The origin of fear about Fridays which land on the 13th of the month is debated.  Some suggest that the origin lies in Christianity.  13 people were described to be at the last supper.  It is thought that Jesus was crucified,  Adam and Eve ate the forbidden fruit, the Great Flood started and the destruction of the Temple of Solomon all supposedly happened on Friday.

A research paper, available on pubmed, originally published in the British Medical Journal, concludes:

"Friday 13th is unlucky for some. The risk of hospital admission as a result of a transport accident may be increased by as much as 52 percent. Staying at home is recommended."

While this may lead some to think the day is indeed unlucky, is it not reasonable to think that we would remember a bad day that happened to land on a Friday the 13th?  Besides that, its a bit of an odd study.   Its authors compared the ratio of traffic volume to the number of automobile accidents on two different days, Friday the 6th and Friday the 13th.  Are traffic accidents more likely if people are nervous and fearful because of the very date on the calendar?  Is Friday the 13th a self fulfilling prophecy?  I am highly skeptical that a simple number on the calendar falling on a simple day of the week could have any influence on anything.  Why would it? There is no mechanism.  This falls squarely in the category of a pseudoscience known as "numerology".  Mathematicians dismiss numerology as having no scientific merit.

Despite that, fear of the number 13 is widespread:

• Many airports skip the 13th gate.
• Most airplanes have no 13th aisle.
• Hospitals and hotels regularly have no room number 13.
• Italians omit the number 13 from their national lottery.
• On streets in Florence, Italy, the house between number 12 and 14 is addressed as 12 and a half.
• Many cities do not have a 13th Street or a 13th Avenue.
• In France, socialites known as the quatorziens (fourteeners) once made themselves available as 14th guests to keep a dinner party from an unlucky fate.
• If you have 13 letters in your name, you may be evil . Jack the Ripper, Charles Manson, Jeffrey Dahmer, Theodore Bundy and Albert De Salvo all have 13 letters in their names.

I did not need to look past a handful of the Ottawa Skeptics user names to find evil among us.  "Halden Johnson," "Michael Waters" and "PatForTesting" all have 13 letters.  Xander Miller and Patrick Roach probably both have middle initials - bringing them into the fold as well.   Did I mention that my ride to the 17th floor of the building I work in was only 16 stories long again today?  As is the case with 80% of highrises, there is no 13th floor.