3 Prevention and Health Promotion
Understand how prevention, health promotion, screening, and systematic evaluation can support better public health action.
Levels of prevention
Prevention aims to avert disease, detect it early, or reduce its effects. The level of prevention depends on the stage of the health problem, the population’s health status, and the intervention’s intended purpose.
acts before a condition or injury occurs by reducing risk or strengthening protection. Examples include vaccination, tobacco-control policies, safer roads, reducing exposure to lead, and promoting physical activity.
Secondary prevention detects a condition early, often before symptoms appear, and intervenes to prevent or slow its progression. For example, for high blood pressure or certain cancers may be followed by appropriate diagnosis and care.
Tertiary prevention limits complications, disability, or loss of quality of life after a condition has been diagnosed. Examples include cardiac rehabilitation after a heart attack, diabetes management to prevent complications, and rehabilitation after an injury.
The categories can overlap. Controlling blood pressure after diagnosis is tertiary prevention because it aims to prevent complications; routine blood-pressure measurement in someone without a diagnosis can be secondary prevention.
enables people to increase control over and improve their health. It takes a broader view than encouraging individual behavior change alone because health is also shaped by social, economic, and environmental conditions.
can build health knowledge and skills, support community participation, and create policies and settings that make healthier choices more achievable. For example, a campaign encouraging walking may be more effective when paired with safe sidewalks, accessible parks, and street design that supports walking. This combination addresses both individual opportunities and community conditions.
and its trade-offs
tests people who do not have recognized symptoms to identify those who may have an increased likelihood of a condition. A positive result is not, by itself, a diagnosis; further assessment may be needed. is generally secondary prevention because it aims to find disease or risk early enough for effective intervention.
Early detection can help when it improves outcomes, but can also cause harm. Possible harms include:
False-positive results, which can lead to anxiety or additional testing.
False-negative results, which can provide misleading reassurance.
Overdiagnosis: finding a condition that would not have caused problems during a person’s lifetime.
A sound program considers evidence for benefit, potential harms, the accuracy of follow-up diagnosis, and whether people can access appropriate care after a result. Recommendations may differ by population and risk, so should follow current, evidence-based guidance rather than assume that more testing is always better.
Planning and conducting
is the systematic collection and analysis of information to understand an intervention, judge its performance, and guide decisions. Planning from the start clarifies what success means and what evidence will be useful.
A practical sequence is:
Assess the context: Identify the health need, setting, resources, affected communities, and factors that could influence results.
Describe the intervention: Specify whom it is intended to reach, what activities it provides, and how those activities are expected to lead to change. A simple can connect resources and activities to short- and longer-term outcomes.
Set questions and design: Decide whether the priority is to understand implementation, assess outcomes, or estimate effects. Select methods that fit the question and setting.
Gather credible evidence: Choose indicators, data sources, and collection methods. Examples include participation records, surveys, interviews, clinical measures, and community-level data.
Interpret findings: Compare results with intended goals, consider alternative explanations and unintended effects, and acknowledge limitations.
Use the findings: Share results with relevant partners and communities, then adapt, continue, expand, or discontinue the intervention as appropriate.
questions and evidence
questions can focus on different aspects of an intervention:
Process: Was the intervention delivered as planned, and who did it reach?
Outcomes: Did knowledge, behavior, access, or health measures change?
Impact or effectiveness: Did the intervention contribute to longer-term health improvements, and how confidently can those changes be attributed to it?
Efficiency: Were resources used appropriately in relation to the results?
No single study design fits every question. Before-and-after measures may show whether an outcome changed, while comparison groups can help assess whether the intervention contributed to that change. Qualitative interviews can explain how people experienced the intervention or why it did or did not work.
Strong also examines whether benefits and burdens differ across groups, involves affected communities in interpreting findings, protects privacy, and uses results for learning and improvement—not just accountability.