With global stock markets roiling and traders appearing to act capriciously on any bit of news, gossip, or innuendo — good or bad — the mere appearance of a day long associated with bad luck may affect world markets today.

Perhaps it's best to stay home. Avoid flying, driving, buying a new television with your economic stimulus check, or acting on a stock tip, on the off chance that this day really is cursed.

If you do, however, then you would be part of the problem, failing to contribute to the global economy just when it needs you most.

"It's been estimated that $800 million or $900 million is lost in business on this day because people will not fly or do business they would normally do," Donald Dossey, founder of the Stress Management Center and Phobia Institute in Asheville, North Carolina, wrote in a 2004 article in National Geographic News.

A date shouldn't matter, of course; but does it? Airlines claim to notice no drop in passenger traffic on these days, although a study published in the British Medical Journal has claimed that traffic accidents increase on Friday 13th.

About one in 15 Americans supposedly suffer from paraskavedekatriaphobia, a "fear of Friday 13th" — the word comes from combining the Greek words Paraskeví (Friday), dekatreís (thirteen), and phobia (fear). Most of these people also suffer from a general fear of the number 13, called triskaidekaphobia.

Despite the Greek terminology, though, actual Greeks (and people in Spanish-speaking countries) consider Tuesday the 13th as their unlucky day, while Italians fear Friday the 17th.

Humans have a long history of fearing inauspicious days. The Romans were superstitious about the Ides of March, the date Julius Caesar was assassinated; the ancient Mayas stayed cowering indoors for the five days at the end of each year that came after their 360-day calendar ended. Called the haab, these were days of extreme bad luck when all activity stopped.

The modern terror over Friday the 13th seems to come from a combination of Christ being crucified on a Friday, and an ancient dislike among mathematicians, numerologists and soothsayers of the number 13.

Judas Iscariot, who betrayed Christ, was the 13th disciple. The number 13 is also considered an imperfect and even evil number because it follows the revered number 12.

Twelve can be reached through doubling six, another favorite number, and by multiplying 4 and 3. There are also 12 months, 12 signs of the Zodiac, and 12 Apostles.

Oh, and there are the Friday the 13th horror movies, featuring Jason in his hockey mask, as well as a related TV series. These haven't helped us feel calm and serene about this day.

Still, maybe those of us who do not suffer from paraskavedekatriaphobia should do our part for the economy and buy more today - more flights, cars, and stocks.

The question is: Do you dare?

by David Ewing Duncan