What does a study's risk number mean for me?
Headlines say 48% lower risk or five times the risk. Put the study's number in with your age and sex to see what it changes in real people.
Why a ratio needs your age
A hazard ratio compares how fast people in two groups died during a study. A ratio of 2 means twice the rate. At 30 that's a tiny number doubled, and at 75 it's a big one. This puts the ratio on the 2024 US life table for your age and sex, so you can see the difference in people out of 1,000.
It applies the ratio to the average person your age, as if they were the study's comparison group. Most studies compare against a group that's healthier or less healthy than average, so read the answer as a sense of scale.
The ratios in the list
| Comparison | Hazard ratio | Who | Study |
|---|---|---|---|
| Smoking 15 to 24 a day, against never | 2.33 | US health professionals | Li et al., Circulation 2018 |
| No exercise, against 3.5 to 6 hours a week | 2 | US health professionals | Li et al., Circulation 2018 (0.50 the other way) |
| Least fit quarter, against the fittest 2% | 5.04 | 122,007 treadmill tests | Mandsager et al., JAMA Network Open 2018 |
| Floor test score 0 to 4, against 10 | 3.84 | 4,282 adults aged 46 to 75 | Araujo et al., European Journal of Preventive Cardiology 2025 |
| Can't stand on one leg for 10 seconds | 1.84 | 1,702 adults aged 51 to 75 | Araujo et al., British Journal of Sports Medicine 2022 |
| Most regular sleepers, against the least regular | 0.52 | 60,977 UK Biobank adults | Windred et al., Sleep 2024 |
| Lifting 90 to 119 minutes a week, against none | 0.87 | 147,374 US health professionals | Zhang et al., British Journal of Sports Medicine 2026 |
One study at a time. The habits in these studies overlap, so ratios from different studies are never multiplied or added.
What your result means and what to do next
Your two numbers are how many of 1,000 people your age and sex would die in the next 10 years, with and without what the study measured. The gap between them is the size of the effect in real people. A gap of a few in 1,000 means the headline is about something small at your age, and a gap of tens means a big one.
Most of these studies followed people rather than testing a change, so the gap is closer to an upper end. When a result looks big, check whether a trial backs it, and put your effort where the gaps are widest, which for most people is smoking, fitness and strength. The simple plan lists them in that order.
7 sources
- NCHS, United States Life Tables, 2024cdc.gov
- Li Y and others, Circulation 2018pmc.ncbi.nlm.nih.gov
- Mandsager K and others, JAMA Network Open 2018jamanetwork.com
- Araujo CG and others, European Journal of Preventive Cardiology 2025academic.oup.com
- Araujo CG and others, British Journal of Sports Medicine 2022pubmed.ncbi.nlm.nih.gov
- Windred DP and others, Sleep 2024pubmed.ncbi.nlm.nih.gov
- Zhang Y and others, British Journal of Sports Medicine 2026pubmed.ncbi.nlm.nih.gov
