A sanitation worker begins cleaning Times Square after the 2014 New Year's Eve celebration. (John Minchillo/AP)

Considering the number of people who make New Year's resolutions — somewhere between 40 and 50 percent of us, according to various reports — there isn't an overwhelming amount of recent research on how successful we are. But as you might not suspect, the data we do have show that 46 percent of us succeed — or say we succeed — for at least six months. Change is hard, but for a while we seem to be able to keep it up.

Still, the speed at which many of us fail is pretty surprising. A 1989 study by John C. Norcross of the University of Scranton shows that 77 percent of resolvers had been able to keep their commitments "continuously for one week," and follow-up research by Norcross in 2002 put the figure at 71 percent for one and two weeks. That means that about 25 percent of us don't stick with it for seven measly days.

People! You can't figure out how to work all the buttons on a treadmill in a week! Give it another whirl.

Alas, it doesn't seem to work that way. At three and four weeks, 64 percent reported continuous success, according to Norcross's 2002 research. That fell to 50 percent after three months and 46 percent after six months. Only 19 percent deemed themselves successful in reaching their goal and sticking to the effort when Norcross followed up his 1989 survey two years later.

Here's some good news, though: At six months, people who make New Year's resolutions are more than 10 times as likely to keep them as people who don't follow the annual tradition. Norcross found that just 4 percent of "non-resolvers" were able to say that they had continuously stuck with an attempt to change something after six months.

What are people trying to change? Again, that won't surprise you. According to a 2012 online Harris poll of 3,036 adults conducted for Norcross's book "Changeology," the top resolutions were weight loss (21 percent), improving finances (14 percent), exercising (14 percent) and getting a new job (10 percent). Cutting back on smoking and improving a relationship were cited by just 5 percent and assertiveness by just 1 percent of the respondents.

But why does a (possibly drunken) New Year's Eve vow work so much better than just setting your mind to something? Here the research is illuminating. Norcross and his colleagues were not available, but in a 2008 interview with National Public Radio, Norcross said: "It's not so much the resolution as it is how attainable or realistic the goal is. You know, someone says I'm going to lose 50 pounds and keep it off this year versus I think I'll struggle to keep 10 off — that's a little more realistic."

"We say, if you can't measure it, it's not a very good resolution, because vague goals beget vague resolutions," he added.

Successful resolutions also begin long before Jan. 1, in what some researchers call the "contemplation phase." That's the period when you develop an attainable goal and the confidence that you can stick with it even if you slip occasionally.

There are things you can do to boost your motivation along the way. One is to tell other people about your goal or involve others in the effort, so that it's more difficult to quit because you'll let people down. Another is to have a serious financial stake in the outcome. George Loewenstein, a behavioral economist at Carnegie Mellon University who has studied financial incentives and weight loss, devised ways to include social support and pressure, competition and money to spur obese veterans to lose weight. In separate four- and eight-month studies, participants lost nearly a pound a week, significantly more than a control group.

But in both efforts, when the money stopped flowing, the weight came back. In the Harris poll, people cited "slipping quietly back into my old routine over time" as the top reason for previous failure.

So hit the gym, put out that cigarette or turn down that piece of  cake again today. Tell someone you're going to do it. Give yourself a tangible reward. Then get out there again tomorrow.

Registered dietitian Sloane Mendelsohn talks with PostTV about some of the dangerous diet fads for 2015. She also explains the best way to quickly and safely lose weight. (The Washington Post)