“…They are often individually tailored and occur as part of complex systems (health and social care, employment, and education) that are prone to modification. They may be influenced by many potential 'confounders' other than the intervention in question: for example, by environmental factors (such as where the intervention takes place and access barriers -for instance, transport), treatment intensity, the therapist's expertise, whether and how feedback is given, and both 'therapist' and 'patient' factors such as personality, warmth, and communication skills, how the patient engages with the therapist and/or process, motivation, and effort (Sherer et al 2007).…”