Health cheat sheet

Health dimensions

Physical, mental and social conditions interact. A health measure captures only part of a person’s experience.

A single test result is not a complete description of health.

Prevention levels

Primary prevention aims to prevent disease; secondary prevention seeks earlier detection; tertiary prevention reduces established disease effects.

Distinguish prevention of onset from reduction of existing complications.

Incidence and prevalence

Incidence counts new cases over a period. Prevalence describes existing cases in a population at a specified time or period.

New cases this year and all current cases answer different questions.

Absolute and relative risk

Absolute risk describes how often an outcome occurs. Relative risk compares risks between groups.

A change from 2 in 100 to 1 in 100 halves relative risk, with a 1-point absolute reduction.

Determinants of health

Health outcomes are influenced by biological, social, economic and environmental conditions as well as services and behaviour. An association at one level may not describe every individual.

Housing conditions and access to care can affect opportunities to maintain health.

Rates need denominators

A count is meaningful only with its population and time frame. Rates and proportions must use a denominator that matches the question and the population at risk.

Compare 20 cases in 1000 people with 20 cases in 100 people before describing frequency.

Confounding

A third variable can be associated with both an exposure and an outcome, creating or distorting an observed relationship. Study design and analysis can reduce, but do not magically eliminate, confounding.

Age can affect both exposure patterns and the frequency of many outcomes.

Interpreting evidence

Compare the study population, measured outcome, uncertainty and study design before applying a finding. Relative changes alone can make small absolute differences sound large.

Ask whether a claim concerns a laboratory marker, symptoms or a longer-term health outcome.

Worked example: absolute difference

In a teaching dataset, 12 of 200 people in one group and 8 of 200 in another have an outcome. Risks are 6% and 4%; the absolute difference is 2 percentage points.

The second group has one-third lower relative risk: (6 − 4) ÷ 6 ≈ 33%.

Common mistake: percentage points

A change from 10% to 15% is an increase of 5 percentage points and a relative increase of 50%. State which measure you mean.

Percent change = (new − old) ÷ old × 100%, when the original value is non-zero.

Check your understanding

A prevalence rises from 4% to 6%. What is the percentage-point increase?

2 percentage points. The relative increase is 50%.

Curriculum connections

Sources