The conceptual framework of a public health PhD is the diagram and written rationale that show which constructs your study examines, how you expect them to relate, and which published models justify that picture. Build it in seven steps: question first, then anchor model, definitions, relationships, measures, scope and a return in the discussion.
What is a conceptual framework in a public health PhD?
In a public health thesis the framework does a particular job. Health outcomes are shaped at several levels at once, from individual behaviour to neighbourhood conditions to national policy, and no single study can examine all of them. The framework is where you decide which parts of that system your thesis actually tests and where you show the examiner that you know what you have left out and why.
It is also not the same thing as a theoretical framework. A theoretical framework is an existing theory or model that you adopt. A conceptual framework is the study-specific structure you assemble, often drawing on one or more existing models. The general distinction, with worked outlines by discipline, is explained in what a conceptual framework is for a postgraduate thesis; this guide applies it to the way public health questions are asked and examined. For a thorough account of how conceptual frameworks are built as a research procedure, Jabareen (2009), “Building a Conceptual Framework: Philosophy, Definitions, and Procedure” in the International Journal of Qualitative Methods, is a citable starting point.
Step 1: Start from the research question, not from a diagram
The most common reason a framework fails in the viva is that it was drawn first and the question fitted to it afterwards. Write the research question in one sentence, then underline the nouns. Each of those nouns is a candidate construct: an exposure, an outcome, a population, a setting or a mechanism. If a box in your diagram does not correspond to something in the question or in a stated aim, remove it.
Public health questions generally take one of three shapes, and the shape tells you what the framework has to show. A question about distribution (who has the problem, and where) needs the determinants that explain the pattern. A question about causation or association needs an exposure, an outcome and the other variables that sit between or around them. A question about implementation or intervention needs the intervention, the context and the pathway by which change is expected to occur.
Step 2: Choose one or two published models to anchor the framework
Examiners expect to see where your framework comes from. Three models appear very often in public health theses, each answering a different kind of question.
- The Dahlgren and Whitehead model of health determinants, often called the rainbow model, arranges determinants in layers around the individual. The authors themselves reflected on its use thirty years on in Public Health (2021), including what it was never intended to do. It describes determinants rather than a causal pathway, so it anchors questions about inequality and distribution well and tests of mechanism poorly.
- The social-ecological perspective as set out by McLeroy and colleagues (1988) in Health Education Quarterly treats behaviour as shaped by influences at several levels and is widely used for programme and intervention questions.
- The Health Belief Model, traced by Rosenstock (1974) in Health Education Monographs and reviewed by Janz and Becker (1984) in Health Education Quarterly, is an individual-level model of health behaviour. It suits a thesis about why people take up or avoid an action, and it fits badly with a question about neighbourhood structure.
Read the original source for whichever you choose and cite it, not a textbook summary of it. If you combine models, say what each contributes: for example, a determinants model for the context and a behavioural model for the individual pathway.
Step 3: Define every construct in one sentence, with a source
List the constructs that survive Step 1 and write a one-sentence conceptual definition for each, citing where the definition comes from. This is the step that turns a picture into an argument. If two constructs seem to overlap, such as “social support” and “social networks”, the definitions force you to say how they differ. The same definitions later feed the instrument matrix, which is explained in building a variable operationalisation matrix with a management example whose logic transfers directly to health constructs.
Step 4: Give every arrow a meaning
An arrow is a claim. Decide what each one asserts and say so in a key or caption. The usual meanings are:
- A causal path from exposure to outcome that your design is able to examine.
- An association you expect but do not claim is causal, which is common in cross-sectional work.
- A mediating pathway, where one construct is expected to carry the effect of another.
- A moderating influence, where a construct changes the strength of a relationship.
In observational public health questions it helps to show confounders explicitly. Greenland, Pearl and Robins (1999), “Causal Diagrams for Epidemiologic Research” in Epidemiology, introduced causal diagrams to epidemiology as a way of deciding which variables to adjust for, and many examiners in population health expect your framework to show why your analysis adjusts for some variables and deliberately not for others.
Step 5: Tie every box to a measure or a line of questioning
For each construct, write the variable that will measure it or, in qualitative work, the topic that will explore it. A framework containing a box you cannot measure or ask about is a decoration. The table below is a fully illustrative example for an invented thesis on neighbourhood green space and wellbeing in older adults in a UK city. It is not a real study.
| Box in the framework | Conceptual definition (illustrative) | How it enters the study |
|---|---|---|
| Access to green space | The distance and ease with which a resident can reach publicly accessible green areas | Residential distance to nearest park from administrative geography |
| Physical activity | Planned and incidental movement in a usual week | Self-reported questionnaire item set |
| Social contact | Frequency and quality of contact with others outside the household | Validated scale chosen and justified in the methods chapter |
| Mental wellbeing | Positive mental functioning and life satisfaction | Validated wellbeing scale, outcome variable |
| Deprivation | Area-level socio-economic disadvantage | Area deprivation index, treated as a confounder |
In this example, physical activity and social contact are drawn as mediating pathways from green space to wellbeing, and deprivation is drawn as a confounder with arrows to both access and wellbeing. Every arrow has a stated meaning, and every box has a definition and a place in the data collection. That is the standard to aim for in your own framework.
Step 6: State what the framework deliberately leaves out
A public health framework can always be criticised for omitting something, so say what you omitted and why. A thesis on neighbourhood green space might leave out air pollution as a competing pathway, noting it as a limitation and a direction for later work. A short paragraph on scope turns an obvious gap into a decision. It also prepares the ground for the limitations section, which the discussion chapter will need.
Step 7: Bring the framework back in the results and the discussion
Examiners read for whether the framework is used. In the results, organise findings by the constructs and relationships in the diagram. In the discussion, say which relationships the data supported, which they did not, and whether the framework should be revised. Presenting a revised diagram at the end is acceptable and often impressive, provided you explain why it changed. The same logic is described for the introduction chapter in how to write a PhD thesis introduction chapter, where the thesis map should already point to where the framework will be tested.
What do examiners ask about a public health framework?
Four queries come up often enough to prepare for.
- “Why this model and not another?” Have a two-sentence answer that names the question the model suits and the question it does not.
- “What level is your unit of analysis?” Individual and area-level constructs should not be mixed in an interpretation without saying so.
- “Where are the confounders?” If your question is about exposure and outcome, the framework should show them.
- “Is this framework tested or assumed?” Be explicit about which relationships your data can speak to.
These sit alongside the other recurring patterns collected in what PhD examiners actually write in their reports.
Frequently asked questions
What is a conceptual framework in a public health PhD?
It is the structure you build to show which constructs your study examines, how you expect them to relate, and which published models and evidence justify that picture. It is usually presented as a diagram plus a written rationale.
Is a conceptual framework the same as a theoretical framework?
No. A theoretical framework is an existing theory or model you adopt; a conceptual framework is the study-specific model you assemble, which may draw on one or several theories.
Can I use the Dahlgren and Whitehead model as my whole framework?
Only if your question is about the layers of determinants. It is a model of determinants rather than a causal pathway, so most theses use it as an anchor and add the specific constructs and relationships they test.
Do I need a diagram?
Examiners expect one for most quantitative and mixed-methods designs because it shows relationships at a glance. Qualitative theses may use a looser map of sensitising concepts, but the written rationale is still required.
How many constructs should the framework contain?
As few as answer the research question. Every box must be defined and linked to a measure or a line of questioning, so a framework with more boxes than you can measure is a warning sign.
What should the arrows mean?
State it in a key or caption: a causal path, an association, a mediating pathway or a moderating influence. Mixing meanings in one diagram without saying so is a frequent examiner query.
Where does the framework go in the thesis?
Usually at the end of the literature review or the start of the methods chapter, and it should reappear in the results and discussion so the findings are interpreted against it.
Should confounders appear in the framework?
For observational questions about exposure and outcome, yes. Many epidemiologists use causal diagrams to show confounders, mediators and colliders, which tells the examiner why your analysis adjusts for some variables and not others.
Can the framework change during the PhD?
Yes, particularly in qualitative and mixed-methods work. If it changes, present the final version in the thesis and explain in the methods or discussion how and why it developed.
Is it acceptable to draw my own model instead of using a published one?
Yes, provided you show the evidence behind each relationship. A framework entirely without published anchors is hard to defend, so say which models or studies informed each part.
From a sketch to a chapter
Most candidates have the framework in their head long before it is on the page, and the gap between the two is where months disappear. Tesify is used by 9,000+ students across 15,000+ chapters to structure a thesis chapter by chapter, and the thesis stays 100% written by you. The constructs, the arrows and the argument for them are yours; the structure helps you see which ones are still missing from the page.