Why test theory fidelity?

Recent guidance about developing and evaluating complex interventions emphasises the need to use theoretical explanations to aid understanding of what works within an intervention. This is in direct contrast to the large research literature about drug studies, where human physiology is used to explain why certain drugs do and do not work in specific people and clinical conditions. This works well, in most cases, because there is consistency of physiology across the human race.

However, in complex interventions (such as adopting a healthy lifestyle), the actual intervention is often composed of several components (dietary and exercise advice, group work, individual goal setting), and is delivered by certain people (GPs, physiotherapists, trainers, coaches) for patients in specific circumstances. The complexity is often multi-layered and acts across several systems; from the healthcare practitioners that deliver it, to patient communities, and to individuals and their families. There is often an element of behaviour change for the staff delivering the intervention, and for the patients receiving it.

This is often a point of confusion, because there are many psychological and sociological theories of behaviour change which can be used to justify or explain a complex intervention. Behavioural theories can act at an individual level (I will continue to exercise because I feel positive benefits), or a group level (I feel more motivated when I discuss healthy eating strategies with my friends). They can also refer to the social environment (It is rewarding seeing other people being healthy around me) or to the physical environment (The gym is easy for me to get to, on my own).

In the current literature, it seems that theories can be chosen to explain why an intervention does or does not work. Sometimes they are offered as an excuse or an isolated explanation.

  • Is this fair – especially if the same theory has not been used to design or implement the intervention?
  • Does this confuse or distort the responsible use of theory in research?
  • Should theory be used faithfully and responsibly in designing and implementing interventions before it can inform evaluation?

If we recognise the power of theories (self-efficacy , adult learning) to explain why certain behaviours (regular exercise, healthy eating) create specific outcomes (fitness, weight loss), then should we expect in high quality research, that the theory has been faithfully used at all stages of designing, implementing and evaluating and intervention? In the same way that poor understanding of basic biochemistry may distort results from drug studies, does a poorly used theory also confuse and distort explanations of complex interventions?

The concept of fidelity was recently introduced for implementing complex interventions. It was suggested that the way the intervention was delivered could influence intended outcomes. Specifically, five elements were identified that could be measured: adherence, exposure, quality, participant responsiveness and programme differentiation. Through measurement, it can be determined how faithfully the implementation was delivered. It was suggested that there could be more confidence in attributing outcomes to faithfully implemented complex interventions.

Using similar arguments,  we may be able to be more confident in using theories to explain and predict outcomes if they are consistently and transparently used to explain why and how complex interventions should be designed, delivered and evaluated.

The next challenge is how do we identify and measure the faithful use of theory in designing, delivering and evaluating complex interventions?




I conduct and supervise research that promotes the translation of quality research evidence for use in clinical practice.

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Posted in behaviour, change, complex interventions, implementation, intervention, realist review, theory fidelity

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