Models of Health and Health Behaviour

1The net under the bed

A family in a malaria-risk area of Rwanda has received insecticide-treated mosquito nets from the health centre. They know that malaria is transmitted by mosquitoes and that nets prevent it. Yet one net stays folded under a bed. The father says it is too hot under the net; the children say they rarely see mosquitoes; nobody has had malaria for two years.

Knowing the facts was not enough. To explain and change such behaviour, health psychology uses models: simplified accounts of which factors matter and how they connect. This lesson compares two models of health in general and three models of health behaviour.

21. Biomedical versus biopsychosocial

Engel (1977) argued that the biomedical model could not explain why two people with the same disease experience it so differently, or why some people with no detectable disease suffer. The biopsychosocial model is now standard in health care. Its weakness is that it can be vague: it says that all three kinds of factor matter, but not how much each matters or exactly how they interact in a given case, which makes it hard to test.

32. The Health Belief Model (HBM)

Developed by American public health researchers in the 1950s and 1960s (Irwin Rosenstock, 1966; Marshall Becker, 1974), the HBM says that whether a person takes a health action depends on his or her beliefs (Figure 1).

Applied to the family: their perceived susceptibility is low ("we rarely see mosquitoes"), a barrier (heat) is high, and there has been no recent cue to action. A health worker could raise susceptibility with local facts, reduce the barrier by showing how to hang the net for airflow, and use cues such as reminders during the rainy season.

Evidence. A meta-analysis by Christopher Carpenter (2010) found that perceived benefits and barriers were the most consistent predictors of behaviour, while perceived susceptibility and severity predicted it only weakly. The HBM is easy to use, but it treats people as rational planners and gives little weight to emotions, habits and social norms.

43. The theory of planned behaviour (TPB)

Icek Ajzen (1991) proposed that the best predictor of behaviour is intention, which depends on three things:

• Attitude towards the behaviour: "Getting tested for HIV is a responsible thing to do."
• Subjective norms: what important others think: "My friends and my parents would approve."
• Perceived behavioural control: "I know where the health centre is, and the test is free and confidential."

A review of 185 studies (Armitage and Conner, 2001) found that the TPB explained on average about 39% of the variation in intentions but only 27% of the variation in behaviour. This intention–behaviour gap is a central problem: Thomas Webb and Paschal Sheeran (2006) found that a medium-to-large change in intention produced only a small-to-medium change in behaviour. Forming specific "if–then" plans (implementation intentions: "If it is 9 p.m., then I will lower the net") helps to close the gap.

54. The transtheoretical model (stages of change)

James Prochaska and Carlo DiClemente (1983), studying people who stopped smoking, described change as a series of stages: precontemplation (not thinking of changing), contemplation (thinking about it), preparation (planning), action (changing) and maintenance (keeping it up, with possible relapse and re-entry). Help should match the stage: information and awareness for precontemplators, practical plans for those in preparation.

The model is popular with health workers, but critics such as Robert West (2005) argue that the stages are arbitrary lines drawn on a continuum, and reviews have found that interventions matched to stages are generally no more effective than unmatched ones.