Religious origins
The ancient Babylonians made promises to their gods at the start of each year that they would return borrowed objects and pay their debts.
The Romans began each year by making promises to the god Janus, for whom the month of January is named.
In the Medieval era, the knights took the "peacock vow" at the end of the Christmas season each year to re-affirm their commitment to chivalry.
At watchnight services, many Christians prepare for the year ahead by praying and making these resolutions.
There are other religious parallels to this tradition. During Judaism's New Year, Rosh Hashanah, through the High Holidays and culminating in Yom Kippur (the Day of Atonement), one is to reflect upon one's wrongdoings over the year and both seek and offer forgiveness. People may act similarly during the Catholic fasting period of Lent, though the motive behind this holiday is more of sacrifice than of responsibility, in fact the practice of New Year's resolutions partially came from the Lenten sacrifices. The concept, regardless of creed, is to reflect upon self-improvement annually.
Participation
At the end of the Great Depression, about a quarter of American adults formed New Year's resolutions. At the start of the 21st century, about 40% did.
Success rate
A 2007 study by Richard Wiseman from the University of Bristol involving 3,000 people showed that 88% of those who set New Year resolutions fail, despite the fact that 52% of the study's participants were confident of success at the beginning. Men achieved their goal 22% more often when they engaged in goal setting, (a system where small measurable goals are being set; such as, a pound a week, instead of saying "lose weight"), while women succeeded 10% more when they made their goals public and got support from their friends.
It is also noted that talking with a counselor about setting goals and new year resolutions can help people keep their resolutions.