Difficulty: Introductory | Prerequisites: None
Health psychology sits at the intersection of biology, behaviour, and social context. This unit lays the groundwork for everything else in the course: the biopsychosocial model that replaces the older biomedical view, the research methods you will see cited in every chapter, and the social determinants that shape who gets sick and who stays well. If you are coming in cold, start here.
Health psychology studies how thoughts, feelings, behaviours, and social context influence physical health. The biopsychosocial model is the field's core framework, replacing the older biomedical view that treated health as purely biological. This unit also covers the research methods used to study health behaviour (and which ones can prove causation), the ethics that govern that research, and the social determinants that explain why wealthier, higher-status people tend to be healthier.
Health psychology
The field devoted to understanding how psychological processes, behaviour, and social factors influence health, illness, and the healthcare system. In simple terms, it is the study of why what you think, feel, and do affects whether you get sick.
Biopsychosocial model
A framework that explains health as the product of three interacting domains: biological (genetics, physiology), psychological (thoughts, emotions, behaviours), and social (culture, socioeconomic status, relationships). Think of it as the replacement for the old "body is a machine" view.
Biomedical model
The traditional Western approach that treats disease as a purely physical malfunction, separate from psychological or social factors. In simple terms, it looks for one biological cause and one biological fix.
Cross-sectional research
A study design that collects data from participants at a single point in time. Think of it as a snapshot: useful for describing what is happening right now, but unable to show change over time.
Longitudinal research
A study design that follows the same participants over multiple time points. In simple terms, it is a series of snapshots of the same people, which lets you track change.
Experimental design
A study in which participants are randomly assigned to conditions and the researcher manipulates an independent variable. This is the only design that can establish causation.
Quasi-experimental design
A design that resembles an experiment but lacks random assignment. Groups are naturally occurring. Think of it as "experiment-like" but without the gold-standard randomisation, so it can show correlation but not prove causation.
Ex post facto / case-control design
Researchers select participants who already differ on a variable of interest and compare them. In simple terms, you start with the outcome and look backward for possible causes.
Prospective study
A study that follows disease-free people forward in time to see whether their behaviours predict later illness.
Retrospective study
A study that starts with people who already have a disease and looks back at their past behaviours.
Ethnography
A research method that seeks to understand a culture from an insider's point of view through immersive observation.
Community-based participatory methods (CBPR)
Research that involves partnering directly with a community so that the people being studied help design and carry out the study.
Descriptive studies
Exploratory research that reports how common something is. Prevalence is how many people have a condition at a given time; incidence is how many new cases appear in a period.
Social determinants of health
The CDC defines these as the conditions in the places where people live, learn, work, and play that affect a wide range of health risks and outcomes. Think of them as everything outside your body that shapes your health.
Health gradient
The consistent pattern in which people with higher socioeconomic status have better health outcomes than those below them, at every level of the ladder.
Clinical efficacy
Whether a manipulated variable causes the observed changes in an outcome under controlled conditions. This is a form of internal validity.
Clinical effectiveness
Whether an intervention works when generalised to a large, real-world sample. This is a form of external validity.
ACEs (Adverse Childhood Experiences)
Abuse, neglect, and other trauma experienced before age 18. The effects are cumulative: four ACEs produce disproportionately worse health outcomes than one. A limitation is that ACE data are typically retrospective.
Health psychology is built on the idea that actions and behaviours influence physical well-being. The field emerged as a counterpoint to the biomedical model, which treated the body as a machine and looked for single biological causes of disease.
The biopsychosocial model proposes three interacting layers:
Bio, the biology of health: genetics, physiology, immune function, neurochemistry.
Psycho , the psychology of health: thoughts, feelings, coping styles, health beliefs, and behaviours such as smoking or exercise.
Social, the social context of health: socioeconomic status, culture, family structure, community resources, and access to healthcare.
The key insight is that none of these layers works alone. A person's biology can predispose them to a condition, their psychology can determine whether they seek treatment, and their social environment can make treatment available or unavailable.
Western biomedicine, which dominates most clinical settings, is evidence-based and technologically advanced, but it is reductionist in philosophy: it looks for the single smallest unit causing illness. The biopsychosocial model does not reject biology. It adds psychological and social factors to the picture.
Cross-sectional: data collected at one point in time. The most common design. Quick and inexpensive, but cannot show change or causation.
Longitudinal: follows the same participants over multiple time points. Can track change, but expensive and participants drop out.
Experimental: the only design that can prove causation. Participants are randomly assigned to conditions and the researcher manipulates an independent variable.
Quasi-experimental: resembles an experiment but groups are naturally occurring, not randomly assigned. Includes three sub-types:
Ex post facto / case-control: select people who already differ on a variable and compare them.
Prospective: follow disease-free people forward in time to see whether their behaviours predict illness.
Retrospective: find people with a disease and look back at their past behaviours.
Quasi-experimental limitations: can show correlation but not causation, and cannot rule out the impact of a third variable.
Case report/study: detailed examination of one individual or a small group.
Archival research: analysis of data that have already been recorded.
Focus group: a small group brought together to discuss a topic in depth.
Observational methods have known weaknesses. The presence of the observer can change behaviour (reactivity). Observer bias means the researcher's own views can colour how they interpret what they see. And these methods can describe behaviour but cannot explain or predict it.
Ethnography: seeks to understand a culture from an insider's perspective through immersive fieldwork.
Community-based participatory methods (CBPR): the researcher partners directly with the community being studied, sharing power over the design and execution of the research.
Descriptive studies: exploratory studies that report prevalence (how many people have a condition) or incidence (how frequently new cases appear).
Four problems make clinical efficacy studies difficult:
The selection problem: who ends up in each group may differ in ways beyond the variable being studied.
Outcome definitions: researchers must agree on what counts as a successful outcome.
Patient expectations: patients who expect to improve may improve regardless of the treatment.
The placebo effect: improvement from a sham treatment, which must be controlled for.
Respect for persons: participants must be treated as autonomous agents and given informed consent.
Beneficence: do no harm. The research must minimise risks and maximise potential benefits.
Justice: the benefits and burdens of research must be distributed fairly. You cannot exclude a group of people from participation without justification.
The American Psychological Association adds three professional standards:
Competence: practitioners must work within the boundaries of their training.
Integrity: honesty and accuracy in research and practice.
Professional and scientific responsibility: maintaining ethical conduct and holding colleagues to the same standard.
The "peeling the onion" metaphor structures how health influences work from the inside out. At the core is the individual's biology. The next layer is individual lifestyle, covering psychological factors. Layers two through four are the social determinants of health.
The CDC defines social determinants of health as the conditions in the places where people live, learn, work, and play that affect a wide range of health risks and outcomes.
Economic stability (employment, income, poverty)
Education (literacy, language, early childhood development)
Social and community context (social cohesion, civic participation, discrimination)
Health and healthcare (access to primary care, health literacy, insurance coverage)
Neighbourhood and built environment (housing, transportation, walkability, environmental conditions)
The health gradient is the observation that health outcomes improve at every step up the socioeconomic ladder, not just at the poverty line. The Whitehall study of British civil servants demonstrated this clearly: people with higher-status jobs had better health than those one rung below, who in turn were healthier than the rung below them. The relationship is a gradient, not a threshold.
The takeaway is that being better off economically is associated with being better off health-wise, and this holds true across the entire income spectrum.
Students often think that quasi-experimental designs can prove causation. They cannot. Only true experiments with random assignment can establish cause and effect. Quasi-experimental designs show correlation and suggest possible causal relationships, but a third variable could always explain the result.
Students frequently confuse clinical efficacy with clinical effectiveness. Efficacy is about internal validity (does the treatment work under controlled conditions?). Effectiveness is about external validity (does it work in the real world with diverse populations?).
Students sometimes assume the health gradient means that only poor people have worse health. The gradient runs across the entire socioeconomic spectrum: middle-income people are less healthy than upper-income people, who are less healthy than the very wealthy.
Students often mix up prospective and retrospective studies. Prospective starts with healthy people and follows them forward. Retrospective starts with sick people and looks backward. A simple mnemonic: prospective = "predict forward"; retrospective = "retrace backward".
⚠️ Know the three components of the biopsychosocial model and be able to give an example of each. This is foundational and likely to appear in multiple questions.
⚠️ Be able to match each research design to what it can and cannot do. The key distinction: only experimental designs prove causation.
⚠️ Know the difference between quasi-experimental and experimental. The single difference is random assignment.
⚠️ Be able to list the five social determinants of health as defined by the CDC.
⚠️ Understand the health gradient as a gradient, not a binary. The Whitehall study is a common exam example.
⚠️ The three ethical principles (respect for persons, beneficence, justice) often appear as a matching or identification question.
⚠️ Be clear on clinical efficacy vs. clinical effectiveness. Efficacy = internal validity. Effectiveness = external validity.
True or False: A quasi-experimental design can prove causation. (False: only true experiments with random assignment can.)
Fill in the blank: The three components of the biopsychosocial model are ______, ______, and ______. (Biological, psychological, social.)
True or False: The health gradient applies only to people living in poverty. (False: it runs across the entire socioeconomic spectrum.)
Fill in the blank: The ethical principle that says research must not harm participants is called ______. (Beneficence.)
True or False: Cross-sectional research collects data at multiple time points. (False: that is longitudinal research. Cross-sectional is one point in time.)
Q: A researcher wants to determine whether a new stress-reduction programme causes lower blood pressure. Which research design should they use, and why?
A: An experimental design with random assignment, because it is the only design that can establish a causal relationship between the programme and blood pressure changes.
Q: What is the key difference between a prospective study and a retrospective study?
A: A prospective study follows healthy people forward in time to see if their behaviours predict illness. A retrospective study begins with people who already have a disease and looks back at their past behaviours.
Q: Name the five social determinants of health according to the CDC.
A: Economic stability, education, social and community context, health and healthcare, and neighbourhood and built environment.
Q: How does the biopsychosocial model differ from the biomedical model?
A: The biomedical model treats health as a purely biological phenomenon and looks for single physical causes of disease. The biopsychosocial model adds psychological factors (thoughts, feelings, behaviours) and social factors (culture, socioeconomic status, community) to the picture, treating health as the product of all three interacting domains.
Q: A study finds that people with higher incomes are healthier than those with lower incomes. Can you conclude that higher income causes better health? Why or why not?
A: No. Without random assignment, you cannot rule out third variables (education, access to healthcare, neighbourhood quality) that may explain the association. This study design shows correlation, not causation.
The biopsychosocial model reappears in every subsequent chapter. When you study stress (Ch. 5), you will see biological stress hormones, psychological appraisal, and social support all interacting, which is the model in action. The social determinants framework connects directly to cultural approaches to health (Ch. 3), where different cultures weight the bio, psycho, and social components differently. Research methods from this unit are the lens through which you evaluate every study cited later in the course: when Ch. 7 discusses health behaviour theories, the critiques often come down to whether the supporting evidence is experimental or correlational.
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