“…Survey and questionnaire studies ( n = 27 alone, n = 29 mixed methods), designed to provide further causal insight, also contain issues of heterogeneity and definition, use pre-set, closed questions and present broad, prima facie reasons for non-attendance, and have been critiqued for obscuring complex causal realities [ 27 , 48 – 51 ]. Studies report issues recruiting patients at risk of missing appointments, who may be less likely to participate in such research [ 42 , 44 , 52 – 59 ]. Some designs actively exclude relevant patient groups—for example, those with existing mental health issues, cognitive impairments, learning disabilities or who do not speak English [ 46 , 48 , 60 – 64 ].…”