Table 2 Supporting evidence for model factors

Favourable organisational and trial context

Optimal organisational and trial contexts that produces a cost-effective, rigorous trial that is easily implemented

➢ Trial setting

➢ Organisational complexity

➢ Scientific rigour

➢ Practical concerns

‘In the NHS study what we saw was more loss to follow-up, more patients not attending treatment.’ (SELF: interview).

‘If money was no object, I’d’ve had someone ring them up every month to get them to send [the diaries] back’ (TOMAS: interview).

• Inhibited or facilitated the use of other factors.

• If unfavourable, this became the researchers’ primary priority

Trial motivators

Tangible and intangible benefits participants received through trial participation (e.g. greater clinical attention)

➢ Initial motivation for participation

➢ Treatment or other effects experienced

➢ Contextual effects (e.g. Hawthorne effect) of trial participation

‘[Control participants’] primary reason … for adhering to the exercise programme … was that they were taking part in a research study and had to record the sessions in a diary’ (ENVISAGE-WP2: trial publication).

SCORD had high retention (96 %), high satisfaction (90 % for researcher phone/email contact and 91 % for visits) and all diaries were returned

• A net beneficial effect of participating appeared to generate a favourable attitude towards the trial, encouraging participants to complete and return all data required

Diary salience

The extent to which the diary was emphasised to participants as a key data collection tool

➢ Initial diary status

➢ Positive and negative effects of diary completion

➢ Ongoing en/discouragement for diary completion

‘The therapist would always try and make sure it was hung up somewhere or out next to the, out next to the telephone or somewhere obvious’ (TOMAS: interview).

‘Something that we have to be careful with diaries on emphasising too much …they either you know lie if you like on the diary, or they feel that guilty they haven’t done it they don’t actually come back and see you’ (SUPER: interview).

• Increased participants’ effort to complete it well

• Increased likelihood that participants would remember to complete it

Activity salience

Distinctiveness of the behaviour carried out by the participants

➢ Actual adherence levels

➢ Integration of the behaviour into daily life

‘You wouldn’t really come back with a diary that said you only had done one set of exercises … I don’t know the patient would come in with that you know’ (SUPER: interview).

‘Some people said that it was very difficult to quantify the amount of conversation, because people would say things like “Och, I talk all day!”’ (NONSPEX: interview)

• A distinctive or frequent behaviour would be remembered more easily

• More adherent participants would want to demonstrate this

Diary complexity

The complexity of the diary design and the information it asked for

➢ Participant perceived burden

➢ Participant actual burden

‘Just to make it as simple as possible … we just wanted to reduce that cognitive load … you just tick whatever exercise you did and that was it, because that’s, that’s really all we were interested in anyway’ (ENVISAGE: interview).

‘[We thought] yep, that’s a 1-pager, simple enough, it fits 3 months’ worth of weekly recording’ (SCORD: interview).

• A more complex and difficult diary would provide more barriers to completion and reduce motivation

Participant capabilities Participant-related factors that influenced the level of diary data collected

➢ Participant impairments

➢ Other demands placed on participants (e.g. employment, social demands, caring)

‘There were a few people who hadn’t filled in the diary because they were physically not able to do it’ (NONSPEX: interview).

‘The carers were the main players in this, completing these diaries … most of them were working full time or caring for grandchildren, children’ (EVIDEM-E: interview).

• Impairments reduced ability to remember and record the exercise

• Other demands reduced diary salience in light of other priorities

Active data retrieval

Strategies used by trials to circumvent the need for participants to be motivated to complete or return the diaries

➢ Collection from participants’ homes

➢ Retrospective missing data completion with a therapist or researcher

➢ Completion assistance at appointments

‘It made it very easy for the patients. And to some extent we came to get the data from them…We weren’t waiting for responses by post’ (SCORD: interview).

‘We set it up that she would collect them on a week-by-week basis. You know we never considered any alternative to that as being er, as being viable’ (NONSPEX: interview).

• These strategies generally achieved high return rates and more complete diary data