Not even a crystal ball can predict how long you’ll live. Your genes and your lifestyle play a huge role, of course. And then there’s chance (anyone can get hit by a bus or fall off a cliff taking a selfie).

But scientists have discovered that certain measurable qualities — and at least one less tangible trait — provide clues to what’s ahead. Here are six to think about.

The rise from the floor test

How easily you can stand up from a sitting position on the floor is linked to how long you’ll stick around, says Jonathan Myers, PhD, a health research scientist at the Palo Alto VA Health Care System and clinical professor of medicine at Stanford University.

Myers and his colleagues asked more than 2,000 adults ages 51 to 80 to sit on the floor, barefoot and legs crossed, without using a hand, knee or object for support, and then try to rise, also unsupported. "This sit and rise test is a surrogate for someone's fitness level," Myers says. "If you stand up without using your hands you get the highest score," he says, a perfect 10. A point is subtracted for each support you need to use, such as a hand or holding onto a chair.

They followed the men and women for about six years. Those who did the best on the test were less likely to die during the follow up period. "What we found was, each point increase in the sit to rise test was associated with a 21 percent improvement in survival." That improvement is impressive, he says.

In all, 974 of the men and women scored 8 to 10, Myers says.

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Grip strength

How's your handshake? If it's strong, that's good news. Researchers tested the hand grip strength of more than 60,000 men at age 45 to 68, then looked at their health 25 years later. The men with the least hand grip strength were more than twice as likely as the men with the most to have a disability 25 years later. Maintaining muscle strength helps people avoid developing limitations and disability, the experts say.

Midlife muscle mass

What might matter more than how much you weigh — studies have found mixed answers to whether obesity and a high body mass index (BMI) are linked with a higher risk of early death — is your overall muscle mass.

In one study, researchers followed more than 3,600 men and women, all over age 55, dividing them into four groups based on their muscle mass. Those with the most were 20 percent less likely to die over the 10- to 16-year followup period than those with the least.

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Walking speed

How fast you can walk predicts longevity, too, researchers have found in many studies. In a meta-analysis of nine published studies involving more than 34,000 men and women ages 65 and older, those who walked the fastest in a controlled test were more likely to be alive than the slower walkers over the follow-up period of up to 21 years. The average speed of participants in these studies was about 3 feet per second. Those who walked 3.3 feet per second had better-than-average survival rates for their age and gender. (Walk length in the studies ranged from 8 feet to 6 meters.)

Declining walking speed may be linked with early death, experts say, and reflects damaged systems, such as lungs, heart and blood vessels.

The walking test should be done in a controlled environment under expert supervision, the researchers caution.

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Eyelid health

If you have yellow fatty deposits on your eyelids, a condition known as xanthelasma, you are at higher risk for a heart attack. Researchers looked at more than 34,000 men and women, following them for up to 33 years. Those who had the condition were 1.4 times more likely to have a heart attack during that period than those who did not and were slightly more likely than those without the eye problem to die. The deposits have been linked with high ''bad'' or LDL cholesterol.

Personality

So much for thinking the happy-go-lucky cheerful person will win the birthday award, says Howard S. Friedman, PhD, distinguished professor of psychology at the University of California Riverside. He leads the Longevity Project, research on how personality affects long-term health. "The Longevity Project found that conscientious individuals — those who are persistent, prudent and responsible — live much longer," he says.

Step back, and it makes perfect sense, he says. Conscientiousness is linked to a host of other components of a healthy life, ''including getting more education, establishing a good marriage, succeeding at work and living a focused, meaningful life."

Measures such as grip strength, he says, reflect health and fitness, so it's not surprising they predict longevity. What's important are patterns, he says. "We look at patterns and trajectories across time. For example, it is a good sign if your physical activity is increasing, even if you were not very active in earlier years. In contrast, if your activity levels are markedly decreasing, it does not help much that you were a jock in college." 

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Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.