Understand the numbers
Learn what a percentage means, who it describes and what it cannot tell you.
Percentages in perspective
Fictional teaching examples. These values are not country data or study findings.
The proportion increased by 5 percentage points. That is a 25% increase relative to the starting proportion.
How is this calculated?
Percentage points = ending percentage − starting percentage. Relative change = (ending − starting) ÷ starting × 100. Equivalent per 1,000 = percentage × 10; this is a scaled illustration, not an observed sample count.
Use the same outcome, comparable populations and the same reference period. This tool does not calculate uncertainty or establish a cause. Gross enrolment ratios, rates and odds ratios are not proportions and do not belong in this calculator.
Always ask: a percentage of whom?
Check the denominator, population, age group, outcome and period. A percentage of GDP is not a percentage of people. A rate per 1,000 live births is not a percentage of the whole population.
Counts, rates and comparisons
A large country can have more events but a lower rate. Compare like denominators and periods. Crude rates also reflect age structure; age-standardised rates use a reference population and answer a different question.
Uncertainty belongs beside the estimate
Use the interval reported by the original source. Missing intervals do not mean an estimate is exact. A statistical association alone does not establish that one factor caused another.
Research checks are separate
A verified reference, peer review and an independent methodological assessment mean different things. No study in this collection is labelled certified, and independent scientific review remains pending.
Further reading
Cochrane: interpreting absolute and relative effects · NLM: database inclusion is not endorsement