Concepts & Frameworks

Absolute risk (AR) is the probability that you experience an event, like a heart attack, a cancer diagnosis, or death, within a defined time period. Relative risk (RR) expresses…

Allostatic load is the cumulative wear and tear your body racks up from adapting to chronic stress. Here is the idea. Your systems keep adjusting to keep you stable, a process…

AMSTAR 2 is a checklist for judging how well a systematic review was conducted. The name stands for A MeaSurement Tool to Assess systematic Reviews, in its second version,…

Antagonistic pleiotropy is an idea from evolutionary biologist George C. Williams, dating to 1957. Here is the idea. A gene that helps you early in life can harm you later, after…

Biological age is an estimate of how old your body seems to be. It is based on physiological and molecular markers, not on the calendar. You can derive it several ways. Options…

Blinding means keeping people involved in a trial from knowing which treatment each participant received. It protects the study after randomisation, in the same way allocation…

A caloric restriction mimetic (CR mimetic) copies some effects of eating less, without you having to cut calories long-term. What effects? It activates AMPK and sirtuins. It…

A centenarian is a person who has reached the age of 100 or more. Centenarians are a key research group in longevity research. Why? Because they tend to delay or escape the major…

Chronological age is simply the time since you were born, usually counted in years. It is the standard reference in demography, medicine, and epidemiology, and it is still one of…

A cohort study follows a defined group of people over time and records who develops the outcome of interest. Exposure is measured first and the outcome later, so the time order…

Compression of morbidity is a concept introduced by James Fries in 1980. It describes a scenario where the onset of chronic disease and disability is pushed back faster than…

A confidence interval is a range of values, calculated from sample data, that is built by a procedure designed to capture the true population value in a fixed proportion of…

Confounding is when a third variable distorts the apparent link between an exposure and an outcome. That third variable is the confounder. It is independently tied to both the…

The Disability-Adjusted Life Year (DALY) is the central metric of the Global Burden of Disease framework. It expresses a population's health loss, including the years you might…

The disposable soma theory, proposed by Thomas Kirkwood in 1977, says your body has to budget its limited energy. It splits resources between maintaining the body (somatic…

An effect size is a quantitative measure of how large a difference or association is, stated independently of sample size. Common forms include the raw mean difference, Cohen's…

Epigenetic drift is the slow, mostly random divergence of DNA methylation patterns over time. It happens between cells, between tissues, and between people, as you age. The…

Frailty is a state of heightened vulnerability to stressors. It comes from deficits piling up across many body systems, which drains your reserve and resilience. Two main ways to…

The free radical theory of aging was proposed by Denham Harman in 1956. It originally blamed aging on one thing. That is the cumulative damage to your cells from oxygen-derived…

Gerontology is the scientific study of aging. It covers the biology, the psychology, and the social side of getting older. It became a formal field in the early 20th century.…

A geroprotector is any drug, supplement, or lifestyle change that targets the basic mechanisms of aging. The goal is to extend your healthspan. Unlike treatments aimed at one…

Geroscience is an interdisciplinary field that studies the biological mechanisms of aging, and how they causally drive chronic disease. Researchers at the Buck Institute coined…

Gompertz law, set out by the British actuary Benjamin Gompertz in 1825, captures a striking pattern: in adults, your risk of dying rises exponentially with age. To be exact, the…

GRADE is a system for rating how certain we can be that an estimated effect is close to the truth. The acronym stands for Grading of Recommendations, Assessment, Development and…

HALE (Healthy Life Expectancy) is a WHO summary measure. It is the average number of years you can expect to live in full health. To get it, you take total life expectancy and…

A hazard ratio (HR) tells you how fast events happen in one group versus a reference group, at any given moment during follow-up. Formally, it is the ratio of the instant event…

Healthspan is the period of your life spent in good health, free from serious chronic disease and major functional impairment. It is conceptually distinct from lifespan, which…

Heritability of lifespan is the share of the variation in age-at-death that comes from inherited genetic differences in a given population. Classic twin studies put it at roughly…

The hyperfunction theory of aging was proposed by Mikhail Blagosklonny in 2006. It offers a different cause of aging. It says aging is driven by growth pathways that stay…

The Kaplan-Meier estimator is a nonparametric way to estimate the survival function, S(t). That is the probability of surviving beyond a given time, t, from time-to-event data…

The mortality plateau (late-life mortality deceleration) is a striking observation. Past about age 105, your risk of dying stops climbing exponentially. Instead it flattens to a…

Lifespan is the total length of time an organism lives, from birth to death, usually expressed in years for humans. At the population level, it is summarized by life expectancy,…

Longevity, Langlebigkeit in German, means more than a long life. It means a longer healthspan, the years lived free of serious chronic disease, within a given lifespan. The word…

Longevity escape velocity is the idea of a tipping point where medicine adds more than a year to your remaining life expectancy for every year that passes, so you would…

Maximum lifespan is the oldest age a member of a species can reach under ideal conditions. It is the documented or theoretical ceiling, not the population's average life…

Mendelian randomization (MR) is a clever way to test cause without a trial. It uses inherited genetic variants (usually SNPs tied to an exposure in a GWAS) as natural stand-ins…

A meta-analysis is a statistical method that quantitatively combines results from multiple independent studies on the same question. It yields a pooled effect estimate, with…

Mortality doubling time (MDT) is how many years it takes for your age-specific risk of dying to double. It comes straight from the Gompertz exponent b: MDT = ln(2)/b. In today's…

Multimorbidity means having two or more chronic conditions at once, with no single one picked as the main disease, say if you have diabetes, arthritis, and heart disease…

Mutation accumulation theory is an evolutionary explanation for why you age. Peter Medawar first proposed it in his 1952 lecture, 'An Unsolved Problem of Biology.' The core idea:…

Negligible senescence describes organisms that show no measurable decline with age. They do not lose function, they do not face a rising risk of death, and they do not lose the…

A network meta-analysis compares three or more treatments at once, including pairs that were never tested head to head. If some trials compared A with B and others compared B…

The number needed to treat (NNT) is the average number of patients you must treat for one extra patient to benefit, versus a control. Laupacis, Sackett, and Roberts introduced it…

An observational study measures what people already do instead of assigning them to do it. Researchers record exposure and outcome and never intervene. Three designs are common:…

An odds ratio compares the odds of an outcome between two groups. Odds are events divided by non-events, not by the total. If 20 of 100 people reach the outcome, the odds are…

The oldest-old is the term for people aged 85 and over. It is the fastest-growing slice of most high-income populations. This group is remarkably mixed in how they fare. A…

A p-value is the probability of obtaining data at least as extreme as the observed data, assuming the null hypothesis and every other model assumption is correct. It is derived…

A placebo is a treatment with no active ingredient, given as a comparison so the effect of the real treatment can be measured against it. The dummy pill, injection or procedure…

Polypharmacy usually means taking five or more medications at once. (Thresholds vary; some use 4 or more, and 'hyperpolypharmacy' is usually 10 or more.) It is not the same as…

Publication bias is the tendency for studies with positive or striking results to be published, and published sooner, while null results stay in the file drawer. The literature…

A Quality-Adjusted Life Year (QALY) is one year of life, weighted by your health-related quality of life. A score of 1.0 means one year in perfect health, and 0 means death.…

A randomized controlled trial (RCT) is an experiment in which participants are assigned to an intervention or a control group by chance. It is the most reliable way to tell…

The rate of living theory proposes that an animal's lifespan is inversely tied to its mass-specific metabolic rate. In short: the faster it burns energy, the sooner it dies. Max…

The reliability theory of aging borrows math from engineering to explain why you age. Leonid and Natalia Gavrilov advanced it in the early 1990s. It models an organism as a…

In gerontology, physical resilience is your capacity to bounce back after an acute health hit. The hit could be an illness, surgery, fall, bereavement, or hospital stay. Whitson…

Reverse causation is when the outcome under study causes the exposure, not the other way around. Observational cohorts record what people do and what happens to them later. They…

A risk ratio divides the probability of an outcome in an exposed group by the probability in an unexposed group. It is also called relative risk. If 20 of 100 sedentary people…

A standardised mean difference expresses the gap between two group means in units of standard deviation instead of the original measurement units. It exists for one practical…

Successful aging is a framework introduced by John Rowe and Robert Kahn (1987, Science), and elaborated in 1997. It distinguishes 'usual' aging, where outside factors pile on top…

A supercentenarian is a person verified to have reached the age of 110 or more. The 110-plus threshold and the term were popularized mainly by L. Stephen Coles, founder of the…

A systematic review answers one clearly stated question by finding, appraising and summarising every study that meets pre-set criteria. What makes it systematic is the protocol:…

An umbrella review is a review of reviews. It collects every systematic review and meta-analysis on a broad topic and compares them side by side, instead of going back to the…