Table 9 Process Evaluation questionnaire measures

Understanding the process of behaviour change

Brief questionnaire piloted/refined with feedback from 15 people and (along with all the newly developed/adapted measures below) validated in a separate study [66]: Covers knowledge about how to make permanent changes to behaviour, how to get and stay motivated, the perceived importance of social support, knowing how to overcome barriers and having skills to manage food cravings (the key processes underpinning the NDPS intervention model).

Explore and enhance motivation [Perceived Importance of lifestyle change]

Perceived importance of eating a healthy diet [with a brief definition provided]: We used a 0 to 10 visual analog scale [VAS] and have also adapted the Intrinsic Motivation Inventory [67, 68] by reducing the number of items to 4 and providing 3 specific intrinsic motivations that should be relevant to the target group and/or which are targeted by the intervention [helping to control my weight; reducing my risk of getting heart disease; contributing to my sense of well-being]. Perceived importance of doing at least 150 min/week of moderate to vigorous physical activity [MVPA]: We also used a 0 to 10 VAS and the same 4 items from the IMI.

Explore and enhance motivation [Confidence about ability to change]

Self-efficacy for healthy eating: we used a 5-item reduced/modified version of the Weight Efficacy Life-Style Questionnaire [69]. We also used a 0 to 10 VAS scale to assess confidence about eating a healthy diet [definition provided] over a] the next month and b] the next 12 months

Self-efficacy for achieving a healthy level of Physical Activity: we use a 5-item physical activity self-efficacy scale [70]. We also used a 0 to 10 VAS scale to assess confidence about being able to achieve a healthy level of physical activity [definition provided] over a] the next month and b] the next 12 months.

Identify and engage sources of social support

Social support for healthy diet: we used a 5-item adaptation of the Sallis et al. scale developed by Norman et al. [71, 72] Social support for healthy level physical activity : we used a 5-item adaptation of the Sallis scale developed by Roesch et al. [71, 73]

Intention Formation

Intention for healthy diet: We developed a brief 4 item measure, using a 5-point Likert scale to assess the level of agreement/disagreement with statements about intention to a) eat healthily and b) adhere to the three main healthy eating recommendations of the programme.

Intention for physical activity: We developed a 3 item measure using 2 items from Sniehotta et al. [74] and a further item about doing moderate intensity activity on 5 days of the week. We used the same 5-point Likert response scale as above.

Action planning

Level of engagement with action planning process. 1. From coding of completed action plans (intervention group only) to indicate level of engagement with the key elements of goal-setting, coping planning and social support planning, as well as participant ratings of how useful the plans/reviewing of plans were. 2. We used 4 items on action planning and 3 items on coping planning from the scale developed by Sniehotta et al. [75]

Self-Regulation (monitoring and problem-solving relating to diet and physical activity)

Frequency of self-monitoring and relapse management activities: We used two pre-existing items on self-monitoring [74], two newly constructed items on attempts to identify and solve problems, and one (new) item on general salience of physical activity aims, all over the last month.

Frequency of weighing: 1 item from Linde et al. [76]

Barriers/problem-solving (intervention group only): We coded progress-review sheets and coping plans used in the intervention under four sub-headings: Practical barriers; People and places; Thoughts and feelings; Other. Level of engagement in this problem-solving activity was defined in terms of the number of items recorded on the written plans in a defined time period prior to measurement.

Empathy/empowerment

Client Satisfaction (intervention group only): Items from the Learning Climate Questionnaire [77] to assess how much empathy/empowerment and engagement participants felt they have with the intervention facilitators.

Quality of intra-group interactions

Physical Activity Group Environment Questionnaire (intervention group only): We selected the 6 items with most face validity for this intervention [78]

Affective response/reinforcement (enjoyment of or other positive reactions to the target lifestyle changes)

Managing impulsive processes (for unhealthy eating)

Body Image Dissatisfaction

Affective response to physical activity: we selected four items from an eight-item version of a Physical Activity Enjoyment Scale (PACES; [68]) Items were selected to represent conceptual diversity [several items in the original scale simply use different words for ‘enjoy’]..

Affective evaluation of eating a healthy diet: We selected two items from the Interest/Enjoyment scale of the Intrinsic Motivation Inventory [67] asking about enjoyment of “healthy foods” [with a definition provided] and added an item asking for level of agreement with the statement “I have found a diet that is both healthy and enjoyable”.

We selected ten items from the 18-item version of the Three Factor Eating Questionnaire [79] These items represent the sub-scales for ‘cognitive restraint’ [all six items] and ‘uncontrolled eating’ [four of nine items],

Perceived Body Image: We used an existing two-items Perceived Body Image questionnaire [79, 80].