By Mark Petticrew

We can surely only get healthier, it would seem, when the public sector, academics and voluntary organisations team up with the food, drinks and leisure sectors to promote healthy living. That’s the claim behind the Government’s Public Health Responsibility Deal.

It has produced lots of practical pledges to help all of us live longer – from labelling drinks so they show alcohol strengths/unit to reducing food portions and supporting active travel. But the road to hell is, as the author and literary critic Samuel Johnson warned, paved with good intentions. So, how do we prove that the Responsibility Deal actually enhances our health and not just the reputations of its participants?

Not easily. We have, in recent years, witnessed some spectacular demonstrations of health improvements following public health interventions. For example, the legislation restricting smoking in public places fed rapidly and measurably through to reduced hospital admissions for heart attacks. In contrast to the simplicity of this success, evaluating the Responsibility Deal faces multiple levels of complexity.

For example, pledges to increase physical activity among young people might not produce health benefits for decades. And, even then, it would be difficult to attribute health gain to this particular intervention.

Likewise, if obesity rates fall, how does one know which, if any, of the many pledges concerning alcohol, food or physical exercise was a key factor? Furthermore, if one wanted to make things really tricky, remember that healthier behaviour in one aspect of life (walking to work) sometimes supports a compensatory shift to unhealthier behaviour in other aspects (a bag of doughnuts on the way home).

But all this complexity should not lead us, in despair, simply to bury our heads in the fridge. The first stage, of course, is verifying that the various promises are being kept. Then, one must build theoretical pathways of how each intervention might, in principle, lead to improved health outcomes.

Take, for example, the pledge to label at least 80 per cent of drinks with clear detail about alcoholic strength in units. We need to check that the consumer sees the label, can read it and can understand it.

Following that, we need to know whether such understanding really reduces alcoholic intake at home (and isn’t, for example, negated by compensatory heavier drinking in the pub). The next step is tracing potential impact of behaviour change on, for example, heart disease, liver damage and so on. At PIRU, which is advising on evaluation of the Responsibility Deal, we have started by building a logic model that graphically shows the potential pathways leading from each of the pledges to their theorised health outcomes. It’s so big that it’s not readable when printed at A4. It would probably squeeze onto a T-shirt – Supersize.

Our first paper, setting out the logic model, the thinking behind it and the implications for evaluation has been submitted for publication. Meanwhile, a second paper will summarise evidence from similar previous voluntary agreements from various sectors that could begin to help refine the pledges as well as the Responsibility Deal overall.

It’s the beginning of a potentially long and complex evaluation. We know that the factors that damage public health are many and that they interact. The menu offered by the Responsibility Deal for a healthier Britain is, likewise, complex. We’re working our way through it.

Dr Mark Petticrew is Professor of Public Health Evaluation at the London School of Hygiene and Tropical Medicine. He is the PIRU lead for the evaluation of public health interventions, including those that extend beyond the NHS.