The effect of choice interventions on retention-related, behavioural and mood outcomes: a systematic review with meta-analysis

Figures & data

Figure 1. PRISMA flow diagram.

Table 1. Details of included studies.

Study	Intervention	Population	Outcome	Comments
Bartley et al. (2016)	Choice intervention (n=29): Choice between one of two beta-blockers Type of intervention: Same class No-choice intervention (n=32): Participants were randomly assigned to one of the two beta-blockers	University students Age (mean, SD): 21.1 (2.78) years 41 females, 20 males New Zealand Two-step RCT	At 1-day: • Anxiety (Mood)
Beer et al. (2017)	Choice intervention (n=29): Choice of exercise mode (bike or treadmill), exercise intensity, duration of exercise (30-60 min), the time of commencement of the session (0600–0900), and the type of music played during exercise, and were provided with cues indicative of choice e.g., ability to change preferences throughout Type of intervention: Combination No-choice intervention (n=29): Participants underwent exercise session with the parameters chosen by their matched partner	Healthy men and women Age (mean, SD): 22 (4) years 20 females, 38 males Belgium Yoked RCT	At immediately post-intervention: • Depression (Mood) • Unhealthy food intake (Behaviour change) • Satisfaction (Retention)
Borland et al. (2013)	Choice intervention (n=758): Choice between either: • QuitCoach – a personalised, automated tailored cessation program that generates two- to four-page letters of advice with suggestions about strategy, both actions and ways of thinking, and encouragement • onQ – a programme that provides a series of text messages that include advice and motivation. The user can interact with it by reporting changes (e.g., a quit attempt) so that appropriate stage-specific messages are sent • Both as an integrated package. Participants could change their minds and take up whatever aspects they wanted. Type of intervention: Same class No-choice intervention (n=2350): Participants were assigned to either the QuitCoach, onQ, or the integrated package groups.	Smokers and recent quitters Age (mean, range): 42.1 (18-80) years 60% female Australia Two-step RCT	At 7-months: • Smoking abstinence (Behaviour change) • Drop-out (Retention) • Adherence to intervention (Retention)
Brenes et al. (2020)	Choice intervention (n=250): Choice between two interventions: • Yoga (20 biweekly group classes) • CBT (10 weekly telephone sessions) Type of intervention: Different class No-choice intervention (n=250): Participants were assigned to either yoga or CBT	Community-dwelling adults 60 years or older, who scored 26 or above on the Penn State Worry Questionnaire-Abbreviated Age (mean, SD): 66.5 (95.2) 86.6% female USA Standard RCT	At end of intervention (11 weeks): • Worry (Mood) • Drop-out (Retention) • Adherence (Retention)
Brown et al. (2013)	Choice intervention (n=not reported): Participants saw two alternative computer monitor backgrounds (circles and triangles) and could choose the one they preferred. Type of intervention: Same class No-choice intervention (n=not reported): Participants saw two alternative computer monitor backgrounds and were randomised to one of them. Participants in both groups were also given or not given expectations about the effect of the background on discomfort.	Undergraduate students Age (mean, SD): 19.54 (2.67) 106 females, 55 males USA Standard RCT	At immediately post-intervention: • Discomfort (Mood)	Results could not be meta-analysed
Carey et al. (2013)	Choice intervention (n=147): Choice between two one-off interventions: • Alcohol101+: interactive CD program with alcohol abuse topics, involves attending a virtual party, decision making, test of knowledge • BMI: intervention session with personalised feedback, estimated typical blood alcohol concentration, information about consequences and risk behaviours, personalised goal and tips Type of intervention: Same class No-choice intervention (n=141): Participants were assigned to either the Alcohol101+ or BMI one-off interventions.	Student drinkers Age (mean, SD): 18.6 (0.71) years 60% male USA Two-step RCT	At 1-month: • Alcohol use (Behaviour change) • Drop-out (Retention) • Satisfaction (Retention)
Castle et al. (2019)	Choice intervention (n=162): Participants were given a choice of self-collected sampling for HPV testing or clinic-based PAP testing. Type of intervention: Same class No-choice intervention (n=321): Participants were assigned to either self-collected sampling for HPV testing or clinic-based PAP testing.	Women between ages of 25 and 64 years Age (mean, median, IQR): Choice arm (45.8; 48; 36–55 years); Self-HPV arm (47.7; 49; 40–56.5 years); Pap arm (45.3; 45; 37–56 years) All female Brazil Standard RCT	At 45 days from initial contact: • Screening uptake (Behaviour change)	Cluster randomisation was used rather than individual randomisation
Chiviacowsky et al. (2012)	Choice intervention (n=14): Participants could choose whether to use a balance pole during a balance test. They could request the pole on any of the 10 trials. Type of intervention: Having or not No-choice intervention (n=14): Participants received the balance pole on the same trial as the person they were matched to in the choice group and told that sometimes they would be able to use it, and sometimes not.	People with Parkinson’s disease Age (mean): choice group 67.92; no-choice group 66.57. Range 46–88 years 13 females, 17 males Brazil Yoked RCT	At immediately post intervention: • Satisfaction (Retention) • Nervousness (Mood)
Clark et al. (2008)	Choice intervention (n=496): Choice between two formats of a programme designed to enhance heart disease management: • Group format: 6–8 women per programme session who met for 2 h/week for 6 weeks, facilitated by a health educator and peer leader • Self-directed format: initial 1-hour orientation, then worked at home on an individual basis over 6 weeks to complete the 6 programme units Type of intervention: Same class No-choice intervention (n=391): Participants were assigned to either group or self-directed formats of the programme	Women aged >60 years with heart disease Age (mean, range): 72.46 (60-90) years All female USA Standard RCT	At 18 months: • Drop-out (Retention)
Goertz et al. (2011)	Choice intervention (n=100): Participants could choose one of three options: classical music, relaxing modern music and smooth jazz. Type of intervention: Same class No-choice intervention (n=75): Participants were assigned to one of the 3 music groups	Hospitalised patients undergoing elective cardiac catheterization Age (mean, SD): 65 (10) years 63 females, 134 males Germany Two-step RCT	At post-intervention (post-operatively): • Anxiety (Mood) • Drop-out (Retention)
Hack et al. (2003)	Choice intervention (n=153): Participant offered choice of receiving audiotape of consultation with oncologist or not Type of intervention: Having or not No-choice intervention (n=321): Participant randomised to not be given audio tape, or given audio tape	Women with a confirmed diagnosis of breast cancer Age (mean, SD): 56.5 (12) years All female Canada Standard RCT	At 12 weeks: • Anxiety (Mood) • Satisfaction (Retention)	Results could not be meta-analysed
Hack et al. (2007)	Choice intervention (n=24): Participant offered choice of receiving audiotape of consultation with oncologist or not Type of intervention: Having or not No-choice intervention (n=48): Participant randomised to not be given audio tape, or given audio tape	Men with a confirmed diagnosis of prostate cancer Age (mean, SD): 67.4 (7.7) years All males Canada Standard RCT	At 12 weeks: • Anxiety (Mood) • Satisfaction (Retention)	Results could not be meta-analysed
Handelzalts and Keinan (2010)	Choice intervention (n=24): Choice of two treatments: • Progressive muscle relaxation: two sessions aiming to reduce physiological arousal. Participants received an audiotape to use at home • Changing of internal dialogue: two sessions of a cognitive behavioural modification technique, aiming to convert negative thought patterns into positive ones Type of intervention: Different class No-choice intervention (n=25): Participants were given instructions that led them to believe they were randomly allocated to the treatments when, in actuality, they were allocated according to their preference.	Students with test anxiety Age (mean, SD): 24.16 (2.55) years 43 females, 30 males Israel Standard RCT	At 2 months: • Anxiety (Mood)	Perceived no-choice
Harkins et al. (2017)	Choice intervention (n=30): Participants could choose between a $20 if they met their step goal more than 5 days a week, or $20 for a charity of their choice, or to share between the two. They could choose their option for the coming week each week, for a total of 16 weeks. Type of intervention: Incentives No-choice intervention (n=48): Participants were randomised to receive $20 if they met their walking goal on more than 5 days per week, or to receive $20 for a chosen charity, for a total of 16 weeks.	Adults aged ≥65 years Age (mean): 80.3 years 57 females, 21 males USA Standard RCT	At end of intervention (16 weeks): • Drop-out (Retention) Average during 16 weeks: • Steps walked (Behaviour change)
Hegerl et al. (2010) SUBSIDIARY PAPERS: Mergl et al. (2011)	Choice intervention (n=82): Participants could select a 10-week treatment with either sertraline or CBT (group format with 5–8 members, 9 sessions at 90 mins each) Type of intervention: Different class No-choice intervention (n=144): Participants were randomised to either sertraline or CBT	Primary care patients with depression Age (mean, SD): 46.4 (14.6) years 251 females, 117 males Germany Standard RCT	At end of intervention (10 weeks): • Depression (Mood) • Drop-out (Retention) • Adherence (Retention)
Inadomi et al. (2012) SUBSIDIARY PAPERS: Liang et al. (2016)	Choice intervention (n=321): Participants had a choice of FOBT (testing kit given for home administration) or colonoscopy (standard information about procedure and directions for bowel preparation were given) Type of intervention: Same class No-choice intervention (n=676): Participants were assigned to FOBT or colonoscopy	Adults at risk of developing colorectal cancer Age (mean, SD): 58.4 (6.9) years 533 females, 464 males USA Standard RCT	At 1 year since enrolment: • Screening uptake (Behaviour change) • Drop-out (Retention)
Johnson et al. (2014)	Choice intervention (n=25): Teachers could choose between one of two strategies for 6 weeks: • Good behaviour game: a group-contingency classroom management procedure designed to reduce problem behaviour in the classroom • Teacher self-monitoring strategy: not defined Both were similar in terms of time and effort required Type of intervention: Different class No-choice intervention (n=44): Participants were assigned to the good behaviour game or teacher self-monitoring for 6 weeks	Teachers working with kindergarten through sixth-grade students Age not reported 88% female USA Standard RCT	At 1 week of implementing the strategy: • Drop-out (Retention) • Adherence to intervention (Retention)	As 88% in the choice group selected the GBG, those who chose TSM were excluded, and those assigned TSM were excluded
Jolly et al. (2011)	Choice intervention (n=100): Participants could choose between 6 weight loss interventions (Weight Watchers, Slimming World, Rosemary Conley, Size Down and two primary care programmes – a nurse led one-to-one support in general practice and one-to-one support by a pharmacist). Interventions were 12 weeks. Type of intervention: Same class No-choice intervention (n=540): Participants were assigned to one of the 6 interventions for 12 weeks.	People registered with general practices with raised BMIs Age not reported 438 females, 202 males UK Standard RCT	At end of intervention (12 weeks): • Weight loss (Behaviour change) • Adherence to the intervention (Retention) • Drop-out (Retention)	Adherence data could not be meta-analysed
Kitchener et al. (2016)	Choice intervention (n=1277): Choice between two interventions to encourage attendance at first cervical screening: • Nurse Navigator (NN): nurses offer support and guidance to discuss concerns/questions, and barriers to screening. Participants receive a letter which included ways to contact the NN and ways the NN could help • Human Papillomavirus self-sampling: participants received a letter offering opportunity to request a SS kit Type of intervention: Different class No-choice intervention (n=2297): Participants were allocated to NN or self-sampling	Women who had not attended their first cervical screen within 6 months of invitation Age not reported All female UK Standard RCT	At 12 months following invitation: • Screening uptake (Behaviour change)	Cluster randomisation was used rather than individual randomisation
Lilliecreutz et al. (2020)	Choice intervention (n=3538): Choice between clinic visit for a pap smear or an HPV self-sampling test kit. Type of intervention: Same class No-choice intervention (n=7076): Participants were allocated to either HPV self-sampling test kit only or routine procedure (invitation to clinic visit for pap smear)	Women that had not participated in the cervical cancer screening programme in the previous 6–8 years Age (range): 30–64 All female Sweden Standard RCT	At 6 months following invitation: • Screening uptake (Behaviour change)
Merrick et al. (2015)	Choice intervention (n=1107): Participants received a screening reminder informing them that if they obtained a mammogram in the next 4 months, they would receive their choice of: • A $15 gift card • Entry into a drawing for $250 gift cards Type of intervention: Incentive No-choice intervention (n=2218): Participants were assigned to receive a $15 gift card or entry into a lottery for a $250 gift card	Adult women with private health insurance Age (mean, range): 53 (50-69) years All female USA Standard RCT	At 4 months following reminder: • Screening uptake (Behaviour change)
Morris et al. (2013)	Choice intervention (n=191): Participants could choose between an online questionnaire, being mailed a paper questionnaire, or being interviewed over the phone Type of intervention: Same class No-choice intervention (n=508): Randomised to one of the 3 questionnaire versions	Women who had reported problems conceiving All females Age (mean, SD): 41.7 (6.1) years UK Standard RCT	Time point unclear: • Drop-out (Retention) • Adherence to intervention (Retention)
Myers and Branthwaite (1992)	Choice intervention (n=48): Participants could choose between two medication schedules: • One dose of amitriptyline 75mg or mianserin 30mg at night • 3 doses of amitryptyline 25mg or mianserin 10mg during the day Treatment was for 12 weeks. Type of intervention: Same class No-choice intervention (n=43): Participants were randomised to one of the two drug routines for 12 weeks.	Outpatients with depression Age (mean, SD): 45.3 (12.75) years 63 females, 28 males UK Standard RCT	At end of intervention (12 weeks): • Drop-out (Retention) • Adherence to the medication (Behaviour change)	Drop-out data could not be meta-analysed
Noël et al. (1998)	Choice intervention (n=305): Participants could choose between two curriculums: • Standard: based on ADA recommendations. Content is 60% non-nutritional management, 40% nutritional management. Includes meal plans and advice to make many dietary changes at once • Experimental: content was 60% nutritional management practices and 40% non-nutritional management. Recommends use of food pyramid instead of meal plan for gradual changes to diet 5 weekly sessions lasting 2 h Type of intervention: Same class No-choice intervention (n=291): Participants were randomised to one of the two curriculums.	Adults with type 2 diabetes Age (mean, SD): 50.7 (10.9) 62.8% female USA Two-step RCT	At 6 months: • Self-care behaviours including exercise sessions per week (Behaviour change) • Drop-out (Retention) At end of intervention (5 weeks) • Adherence to intervention (Retention)	Exercise and drop-out could not be meta-analysed
Olson et al. (2011)	Choice intervention (n=30): Participants could choose between 7 target health behaviours (oral hygiene, hand hygiene, fruit and veg consumption, sweet consumption, whole milk and red meat consumption, transportation safety, exercise). Participants either had self-management skills training or no self-management skills training. Type of intervention: Other No-choice intervention (n=30): Participants had no choice of target behaviour, and either received or didn't receive self-management skills training. Participants were yoked so the behaviour they were assigned to depended on what the choice group picked.	Employees of a large university and teaching hospital and residents from the neighbouring community Age (mean, SD): 31.1 (9.52) years 51 females, 9 males USA Yoked RCT	At the end of intervention (2 weeks): • Behaviour change across the 7 behaviours (Behaviour change) • Adherence to intervention (Retention)	Adherence could not be meta-analysed
Patall et al. (2014) STUDY A	Choice intervention (n=44): Participants could choose the topic (e.g., film trivia or iconic literature) and difficulty (e.g., medium or mix of easy, medium and difficult) of an anagram puzzle game Type of choice: Combination No-choice intervention (n=44): Participants were allocated to a topic and difficulty based on yoked participants in the choice group.	College students Age (range): 18–31 60 females, 28 males USA Yoked RCT	At immediately post-manipulation: • Satisfaction (Retention)	Perceived choice
STUDY B	Choice intervention (n=80): Participants could choose the topic (e.g., film trivia or iconic literature) and how the time would be allotted (e.g., 2 min per puzzle or 16 min for the total game) of a word puzzle Type of choice: Combination No-choice intervention (n=80): Participants were allocated to a topic and time allocation based on yoked participants in the choice group.	College students Age (range): 18–35 107 females, 53 males USA Yoked RCT	At immediately post-intervention: • Satisfaction (Retention)	Mix of actual and perceived choice
STUDY C	Choice intervention (n=70): Participants could choose the specific game they wanted to play, how the time would be allotted, and the difficulty level Type of choice: Combination No-choice intervention (n=70): Participants were allocated to a game, time allocation and difficulty based on yoked participants in the choice group.	College students Age (range): 18–29 88 females, 52 males USA Yoked RCT	At immediately post-intervention: • Satisfaction (Retention)	Mix of actual and perceived choice
Patall and leach (2015)	Choice intervention (n=50): Participants were asked if they would rather play a word game or maths game, and whether they would like the difficulty to be all at medium, or a mixture of easy, medium and difficult. Additionally, participants were told that they could work on the puzzles in any order and take as much or as little time as they wanted. Type of intervention: Combination No-choice intervention (n=50): Participants were assigned to either the word or maths game, and the difficulty assortment based on yoked choice participants. Additionally, participants were told that they should work on the puzzles consecutively and to keep track of their time.	College students Age (range): 18–28 years 70 females, 30 males USA Yoked RCT	At immediately post-intervention: • Satisfaction (Retention)
Pearson et al. (2005)	Choice intervention (n=100): Participants could choose to watch a video or not. The video contained information on (1) the purpose of the procedure, (2) preparing for a colonoscopy, (3) the procedure itself, (4) potential complications, and (5) the postoperative period. Type of intervention: Having or not No-choice intervention (n=99): Participants were randomised to watch the same video or not.	Consecutive patients scheduled to undergo colonoscopy Age (mean, SD): choice group video: 59.8 (13.5), Choice no-video: 59.7 (14.6); no choice video 57.2 (15.4); no choice no video 58.6 (15.8) 79 males Australia Two-step RCT	At 1 week (immediately before procedure): • Anxiety (Mood) • Satisfaction (Retention) • Drop-out (Retention)	Mood outcomes could not be meta-analysed
Rakowski et al. (2003)	Choice intervention (n=403): Choice between 3 reminder strategies: • Reminder letter sent 2 months before the next due mammogram • A 2 month follow up after keeping the scheduled mammogram • A 10 month follow up after keeping the scheduled mammogram. The materials in the 2 and 10 months follow ups included a letter based on apparent barriers to screening, and a tip sheet. Type of intervention: Same class No-choice intervention (n=1211): Participants were randomised to one of the three methods.	Women aged 50–74 Age: 73.3% 50-64; 26.7% 65–74 All female USA Standard RCT	At 15 months since scheduled mammogram: • Screening uptake (Behaviour change)
Raposo et al. (2020)	Choice intervention (n=90): Choice between 3 incentives for increasing walking: • Personal (participants receive 2 cents for every step they increase their daily step average) • Loved one (a loved one receives the money) • Charity (a charity receives the money) Type of intervention: Incentives No-choice intervention (n=270): Participants were randomised to one of the three incentives.	Community-residing adults Age (mean, SD): choice group: 52.29 (19.30); no choice group 51.8 (19.75) 49.7% female USA Standard RCT	At end of intervention (2 weeks): • Step count (Behaviour change)
Rokke et al. (1999)	Choice intervention (n=15): Choice between two treatments • Self-Management Therapy (SMT) behavioural target: 10 weekly hour-long individual sessions, focused on self-monitoring, self-evaluation, and self-reinforcement, with a focus on activity change • SMT cognitive target – same format, and same 3 components, but focused on participant thought Type of intervention: Same class No-choice intervention (n=20): Participants were yoked to the choice group participants	Older adults with depression Age (mean, SD): choice group: 68 (5.7); no-choice group 63 (3.3) 15 females, 25 males USA Yoked RCT	At end of treatment (10 weeks): • Depression (Mood) • Drop-out (Retention)	Depression results could not be meta-analysed
Rose et al. (2014)	Choice intervention (n=27): Participants could choose one of the two treatments (looking at a blue or a green colour). They were told these would reduce discomfort when listening to aversive sounds Type of intervention: Same class No-choice intervention (n=25): Participants were told the treatment had been chosen for them and were randomly assigned to one of the two colours	Undergraduate students Age not reported Gender not reported USA Two-step RCT	At immediately post intervention: • Discomfort (Mood)
Rose et al. (2012)	Choice intervention (n=not reported): Participants could choose one of two products (inert ointments that were described as pain-relieving ointments) to try during a cold pressor task Type of intervention: Same class No-choice intervention (n=not reported): Participants randomly assigned to one of the two products	Undergraduate students Age not reported 25 females, 16 males USA Two-step RCT	At immediately post intervention: • Anxiety (Mood)	Results could not be meta-analysed
Rotton and Shats (1996)	Choice intervention (n=not reported): Choice of 4 out of 20 movies to watch on the two days following surgery. Movies were humorous or serious, and some participants read an article describing the benefits of humour whereas some read an article about the benefits of exciting movies. Type of intervention: Same class No-choice intervention (n=not reported): Participants were yoked to choice participants and they were asked to watch a movie that a choice participant had selected	Patients about to have orthopaedic surgery Age (mean, SD): 43.03 (9.84) years 39 females, 39 males USA Yoked RCT	At immediately post intervention (2-days post-surgery): • Distress (Mood)	Results could not be meta-analysed
Scott et al. (2004)	Choice intervention (n=62): Participants were offered a choice of screening methodology: • Colonoscopy • Computed tomographic colonography Type of intervention: Same class No-choice intervention (n=122): Participants were randomised to received either colonoscopy or CT colonography	Adults from the general community who were asymptomatic and average-risk Age: Between 50–54 years – 91; between 65–69 years 93 69 females, 115 males USA Standard RCT	At immediately following the procedure: • Satisfaction (Retention)	Results could not be meta-analysed
Segnan et al. (2005) SUBSIDIARY PAPERS: Senore et al. (2010)	Choice intervention (n=3631): Choice between: • FOBT: a letter that included a paper slide for stool smearing and instructions for performing the test and for storing and returning the sample or that invited the patient to contact his or her GP or the screening centre to obtain an FOBT kit and instructions • Once-only sigmoidoscopy: offered an appointment for a sigmoidoscopy at a specified time and were asked to call the screening centre to confirm, modify, or cancel their appointment Type of intervention: Same class No-choice intervention (n=12,006): Participants were assigned to FOBT by mail, FOBT by GP or once-only sigmoidoscopy	Adults aged 55–64 years with an average risk of colorectal cancer Age: 50.3% 55-65; 49.7% 60–64 years 14,173 females, 12,509 males Italy Standard RCT	Time-point unclear: • Screening uptake (Behaviour change)
Silberman (2007)	Choice intervention (n=36): Participants had choice of 4 positive interventions that they believed would bring the most pleasure, engagement and meaning to their lives Type of intervention: Same class No-choice intervention (n=36): Participants were matched based on depression scores to a participant in the choice group, and received the same intervention as their choice group partner chose	Undergraduate students Age (mean, SD): Choice group: 19.7 (1.2); no-choice group: 19.6 (1.1) 41% male USA Yoked RCT	At 1 week: • Drop-out (Retention) • Depression (Mood)	Depression results could not be meta-analysed
van Weert et al. (2005)	Choice intervention (n=40): Patients could compose their own program from four components (individual exercise, sports, information and psychoeducation), as judged beneficial to them. The programme was 15 weeks. Type of intervention: Same class No-choice intervention (n=41): Participants received all 4 components in a 15-week programme.	Cancer survivors with different diagnoses Age (mean, SD): 51.6 (9.3) 84% female Netherlands Standard RCT	At end of intervention (15 weeks): • Emotional problems (Mood) • Satisfaction (Retention) • Drop-out (Retention)	Mood and satisfaction results could not be meta-analysed 80% of choice participants selected all 4 components
Veitch and Newsham (1998) SUBSIDIARY PAPERS: Veitch and Newsham (1998)	Choice intervention (n=47): Participants could choose the lighting setting for the day that they would be working under Type of intervention: Same class No-choice intervention (n=47): Participants worked under the lighting conditions chosen by their yoked partner in the choice condition. At the end of the day, they were asked what lighting conditions they would have preferred, but they were unaware that other participants had selected the lighting for the day.	Office workers Age (range): 18–62 All female Canada Yoked RCT	At immediately post manipulation: • Pleasure (Mood) • Satisfaction (Retention)
Wallston et al. (1991)	Choice intervention (n=37): Participants were told that they could choose which of 3 standard antiemetic regimens they would prefer having for four chemotherapy sessions. Each was described including possible side effects. Type of intervention: Same class No-choice intervention (n=37): Participants were given an antiemetic based on the choice of their yoked partner in the choice condition	People undergoing chemotherapy Age (mean, range): 51.9 (25-78) years 62% female USA Yoked RCT	At end of intervention (after 4 sessions): • Anxiety (Mood) • Negative mood (Mood)	Results could not be meta-analysed
Yancy et al. (2015) SUBSIDIARY PAPERS: Mcvay et al. (2014), Mcvay et al. (2016)	Choice intervention (n=105): Participants could choose one of two diets for 48 weeks. They were advised which diet would best fit their preferences based on a questionnaire. Type of intervention: Same class No-choice intervention (n=102): Participants were assigned to a diet for 48 weeks.	Outpatients with a body mass index of at least 30 kg/m2 Age (mean, SD): 55 (11) 27% female USA Two-step RCT	At end of intervention (48 weeks): • Weight loss (Behaviour change) • Public distress (Mood) • Drop-out (Retention) • Adherence to intervention (Retention)
Zoellner et al. (2019) SUBSIDIARY PAPERS: Le et al. (2014)	Choice intervention (n=97): Choice between two PTSD treatments: • Prolonged exposure: the psychotherapy was delivered in 10 weekly 90-to 120-minute sessions according to a manual • Sertraline: participants met with a psychiatrist for ten 30-minute weekly sessions. The dosage was started at 25mg/day with the goal of 200 mg/day Type of intervention: Different class No-choice intervention (n=103): Participants were randomised to either prolonged exposure therapy or sertraline	People with post-traumatic stress disorder Age (mean SD): 37.41 (11.30) years 75.5% female USA Two-step RCT	At the end of the intervention (10 weeks): • Anxiety (Mood) • Adherence to intervention (Retention) • Drop-out (Retention)

Figure 2. Drop-out.

Table 2. GRADE evidence summary: Retention, behaviour change and mood.

Outcome	No of participants (studies) time period	Quality of the evidence (grade)	Relative effect (95% ci)	Anticipated absolute effects
				Risk with no-choice	Risk difference with choice (95% ci)
Retention
- Drop-out	8329 (17 studies) Immediately post intervention-18 months	⊕⊕⊝⊝ LOW^1,3 due to risk of bias, imprecision	RR 0.68 (0.54–0.85)	146 per 1000	47 fewer per 1000 (from 22 fewer to 67 fewer)
- Adherence	5400 (8 studies) 1–48 weeks	⊕⊝⊝⊝ VERY LOW^1,2,3 due to risk of bias, inconsistency, imprecision	RR 1.15 (1.01–1.3)	581 per 1000	87 more per 1000 (from 6 more to 174 more)
- Satisfaction	1113 (9 studies) Immediately post intervention-2 months	⊕⊕⊕⊝ MODERATE^1 due to risk of bias	-	The mean satisfaction score in the control group was 4.50	The mean satisfaction in the intervention groups was 0.13 standard deviations higher (0–0.26 higher)
Behaviour change
- Dichotomous outcomes	35,275 (10 studies) 2 weeks-15 months	⊕⊝⊝⊝ VERY LOW^1,2,3 due to risk of bias, inconsistency, imprecision	RR 1.22 (1.04–1.42)	317 per 1000	70 more per 1000 (from 13 more to 133 more)
- Continuous outcomes	1622 (6 studies) Immediately post intervention-48 weeks	⊕⊕⊝⊝ LOW^1 due to risk of bias, inconsistency	-	The mean total behaviour change in the control groups was 578.84	The mean total behaviour change in the intervention groups was 0.02 standard deviations higher (0.16 lower to 0.2 higher)
Mood	1590 (11 studies) Immediately post intervention-48 weeks	⊕⊕⊝⊝ LOW^1 due to risk of bias	-	The mean total mood score in the control groups was 7.87	The mean total mood score in the intervention groups was 0.02 standard deviations lower (0.14 lower to 0.09 higher)

¹ Downgraded once if the majority of studies were judged as having some concerns, and twice if the majority of studies were high risk of bias.

² Downgraded once for serious heterogeneity (50–74%) and twice for very serious heterogeneity (≥75%).

³ Downgraded once for serious imprecision and twice for very serious imprecision using the values of RR = 0.8 and 1.25 for dichotomous outcomes, and 0.5× the mean control group SD for continuous outcomes.

Figure 3. Adherence.

Figure 4. Satisfaction.

Notes: Beer et al., 2017: The intrinsic motivation inventory – enjoyment subscale; Carey et al., 2013: client satisfaction based on a 5-point likert scale; Chiviacowsky et al., 2012: single item regarding enjoyment; Patal et al., (2014) Studies A–C and Patall & Leach, 2015: Interest-enjoyment subscale of the Intrinsic Motivation inventory; Pearson et al., 2005: patient satisfaction based on a 5-point likert scale; Veitch & Newsham, 2000: Environmental Satisfaction scale.

Figure 5. Total behaviour change: dichotomous outcomes.

Figure 6. Total mood.

Notes: Bartley et al. 2016: short-form State-Trait Anxiety Inventory; Beer et al., 2017: Profile of Mood States – Adolescent Inventory; Brenes et al., 2020: Penn State Worry Questionnaire-Abbreviated; Chiviacowsky et al., 2012: non-validated questionnaire; Goertz et al., 2011: State-Trait Anxiety Inventory – State; Handelzalts & Keinan, 2010: Sarason’s Test Anxiety; Hegerl et al., 2010: Hamilton Depression Rating Scale; Rose et al., 2014 A: aggregated likert scales for irritated, uncomfortable and unpleasant; Veitch & Newsham, 2000: non-validated questionnaire – pleasure subscale; Yancy et al., 2015: Impact of Weight on Quality of Life-Lite questionnaire – distress subscale; Zoellner et al., 2019: Spielberger State-Trait Anxiety Inventory.

Table 3. Risk of bias ratings per outcome.

Authors	Outcome	Randomisation process	Deviations from the intended intervention	Missing outcome data	Measurement of the outcome	Selection of the reported result	Overall bias
Bartley et al. (2016)	Anxiety	Low risk	Low risk	Low risk	High risk	Some concerns	High risk
Beer et al. (2017)	Unhealthy food intake	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
	Satisfaction	Some concerns	Low risk	Low risk	High risk	Some concerns	High risk
	Depression	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
Borland et al. (2013)	Smoking abstinence	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
	Adherence	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
	Drop-out	Some concerns	Low risk	Low risk	Low risk	Low risk	Some concerns
Brenes et al. (2020)	Worry	Some concerns	Low risk	Some concerns	Some concerns	Some concerns	Some concerns
	Drop-out	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
	Adherence	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
Carey et al. (2013)	Drinks per drinking day	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
	Satisfaction	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
	Drop-out	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Castle et al. (2019)	Screening uptake	High risk	Low risk	Low risk	Low risk	Some concerns	High risk
Chiviacowsky et al. (2012)	Satisfaction	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
	Nervousness	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
Clark et al. (2008)	Drop-out	Low risk	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Goertz et al. (2011)	Anxiety	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
	Drop-out	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Handelzalts and Keinan (2010)	Anxiety	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
Harkins et al. (2017)	Daily steps	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
	Drop-out	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Hegerl et al. (2010)	Depression	Low risk	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
	Drop-out	Low risk	Some concerns	Low risk	Low risk	Some concerns	Some concerns
	Adherence	Low risk	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Inadomi et al. (2012)	Drop-out	Low risk	Some concerns	Low risk	Low risk	Some concerns	Some concerns
	Screening uptake	Low risk	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Johnson et al. (2014)	Adherence	Some concerns	Some concerns	High risk	Low risk	Some concerns	High risk
	Drop-out	Some concerns	Some concerns	High risk	Low risk	Some concerns	High risk
Jolly et al. (2011)	Weight loss	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
	Drop-out	Low risk	Some concerns	Low risk	Low risk	Low risk	Some concerns
Kitchener et al. (2016)	Screening uptake	High risk	Low risk	Low risk	Low risk	Low risk	High risk
Lilliecreutz et al. (2020)	Screening uptake	Some concerns	Low risk	Some concerns	Low risk	Some concerns	Some concerns
Merrick et al. (2015)	Mammogram uptake	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
Morris et al. (2013)	Adherence	Some concerns	Low risk	High risk	Low risk	Some concerns	High risk
	Drop-out	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
Myers and Branthwaite (1992)	Adherence to medication	High risk	Low risk	Low risk	Some concerns	Some concerns	High risk
Noël et al. (1998)	Adherence	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
Olson et al. (2011)	Behaviour change	Some concerns	Some concerns	Low risk	High risk	Some concerns	High risk
Patall et al., (2014) STUDY A	Satisfaction	Some concerns	Low	Low	Some concerns	Some concerns	Some concerns
Patall et al., (2014) STUDY B	Satisfaction	Some concerns	Low	Low	Some concerns	Some concerns	Some concerns
Patall et al., (2014) STUDY C	Satisfaction	Some concerns	Low	Low	Some concerns	Some concerns	Some concerns
Patall and Leach (2015)	Satisfaction	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Pearson et al. (2005)	Satisfaction	Low risk	High risk	High risk	Some concerns	Some concerns	High risk
	Drop-out	Low risk	High risk	Low risk	Low risk	Some concerns	High risk
Rakowski et al. (2003)	Repeat screening	Some concerns	Low risk	High risk	Low risk	Some concerns	High risk
Raposo et al. (2020)	Increase in steps	Some concerns	Low risk	Low risk	Low risk	Some concerns	Some concerns
Rokke et al. (1999)	Drop-out	High risk	Some concerns	Low risk	Low risk	Some concerns	High risk
Rose et al. (2014)	Discomfort	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
Segnan et al. (2005)	Screening uptake	Low risk	Low risk	Low risk	Low risk	Some concerns	Some concerns
Silberman (2007)	Drop-out	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
van Weert et al. (2005)	Drop-out	Some concerns	Some concerns	Low risk	Low risk	Some concerns	Some concerns
Veitch and Newsham (2000)	Satisfaction	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
	Pleasure	Some concerns	Low risk	Low risk	Some concerns	Some concerns	Some concerns
Yancy et al. (2015)	Weight loss	Low risk	Some concerns	Low risk	Low risk	Low risk	Some concerns
	Drop-out	Low risk	Some concerns	Low risk	Low risk	Low risk	Some concerns
	Adherence	Low risk	Some concerns	Low risk	Low risk	Low risk	Some concerns
	Distress	Low risk	Some concerns	Low risk	Low risk	Low risk	Some concerns
Zoellner et al. (2019)	Adherence	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
	Anxiety	Low risk	Low risk	Low risk	High risk	Low risk	High risk
	Drop-out	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk

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Data availability statement

All available data including the study protocol, completed data extraction tables for all included studies, and raw data including sensitivity analyses and subgroup analyses are available here: https://osf.io/b27jd/.