Summary of included studies
| Authors (country) | RCT design | Setting | Intervention(s) | Comparator | Participants | Recruited to intervention(s) | Recruited to comparator | Risk of bias* | Comments† |
|---|---|---|---|---|---|---|---|---|---|
| Avenell et al (UK)16 | Parallel group | Secondary care | Open trial design comparing vitamin D, with calcium, with vitamin D and calcium, with no tablets | Conventional trial comparing vitamin D, with calcium, with vitamin D and calcium, with placebo | Patients aged ≥70 attending a fracture clinic or orthopaedic ward | 134/180 (74.4%) | 233/358 (65.1%) | A | Between-group difference was statistically significant (OR 1.56; 95% CI 1.05 to 2.33) |
| Bentley and Thacker (USA)17 | Factorial | University (multicentre, n=5) | A: Info on a high-risk trial for a drug not yet tested on humans, pays $1800 | Not applicable | Pharmacy students | Unclear | Not applicable | C | Assessed willingness to take part in hypothetical studies by risk and reward; did not differentiate recruitment rates between groups (270 participants); between-group differences were statistically significant for both risk level (p<0.0005) and level of payment (p=0.015) |
| B: Info on a high-risk trial for a drug not yet tested on humans, pays $800 | Unclear | ||||||||
| C: Info on a high-risk trial for a drug not yet tested on humans, pays $350 | Unclear | ||||||||
| D: Info on a medium-risk study for a generic drug already on the market, pays $1800 | Unclear | ||||||||
| E: Info on a medium-risk study for a generic drug already on the market, pays $800 | Unclear | ||||||||
| F: Info on a medium-risk study for a generic drug already on the market, pays $350 | Unclear | ||||||||
| G: Info on a low-risk study measuring the salivary levels of stress hormones, pays $1800 | Unclear | ||||||||
| H: Info on a low-risk study measuring the salivary levels of stress hormones, pays $800 | Unclear | ||||||||
| I: Info on a low-risk study measuring the salivary levels of stress hormones, pays $350 | Unclear | ||||||||
| Cooper et al (UK)18 | Parallel group | Secondary care | Partially randomised patient preference design allocating to medical management or transcervical resection of the endometrium or preferred option | Conventional RCT design allocating to medical management or transcervical resection of the endometrium | First time attendees at a gynaecological clinic | 90/135 (96.3%) | 97/138 (70.3%) | A | No information on statistical significance given |
| Coyne et al (USA)19 | Cluster | Secondary care (multicentre, n=44) | Easy-to-read consent statements (altered text style, layout, font size, vocabulary; reading level 7th–8th grade) | Standard consent statements | Patients eligible for participation in a cancer treatment trial | 75/89 (84.3%) | 68/137 (49.6%) | C | Involved consent statements for three cancer treatment trials (one lung, two breast cancer); actual accrual to the parent studies was not significantly different (p=0.32) |
| DiGuiseppi et al (USA)20 | Parallel group | Health Maintenance Organisation (HMO) (multicentre) | Telephone administered questionnaire on hazardous drinking and willingness to participate in lifestyle intervention | Face-to-face administered questionnaire on hazardous drinking and willingness to participate in lifestyle intervention | Patients aged ≥18 attending the HMO with an acute injury | 64/99 (64.6%) | 190/370 (51.4%) | C | Considered different methods of screening, which included willingness to participate in a hypothetical trial; the telephone group was somewhat more often associated with willingness to participate (OR 1.49; 95% CI 0.97 to 2.30) |
| Du et al (USA)21 | Parallel group | Secondary care | 18 min educational video giving an overview of clinical trials and the importance of cancer clinical research to society | Standard care (ie, normal first visit to the oncologist) | Patients aged 21–80 attending a multidisciplinary lung clinic at a cancer centre | 11/63 (17.5%) to therapeutic trials; 16/63 (25.4%) to all trials | 7/63 (11.1%) to therapeutic trials; 10/63 (15.9%) to all trials | B | Considered recruitment to a range of cancer trials categorised into ‘therapeutic’, and ‘therapeutic and non-therapeutic’; between-group difference was not statistically significant for therapeutic trials (p=0.308) or for all trials (p=0.187) |
| Du et al (USA)22 | Parallel group | Secondary care | 18 min educational video giving an overview of clinical trials and the importance of cancer clinical research to society | Standard care (ie, normal visit to the oncologist) | Women aged 21–80 attending a breast cancer clinic at a cancer centre | 10/98 (10.4%) | 6/98 (6.1%) | C | Between-group difference was not statistically significant (p=0.277) |
| Ellis et al (Australia)23 | Parallel group | Secondary care | Information booklet explaining trials, how treatment is selected in an RCT, discussion of treatment options, advantages and disadvantages of participation, where to get more info plus usual discussion about treatment options from the clinician, inc. RCTs if appropriate (no standardisation of what is discussed) | Usual discussion about treatment options from the clinician, inc RCTs if appropriate (no standardisation of what is discussed) | Women undergoing definitive surgery for early stage breast cancer at a cancer institute | 12/30 (40.0%) at follow-up | 14/30 (46.7%) at follow-up | C | Studied willingness to participate in a hypothetical trial; between-group difference was statistically significant (p=0.05) |
| Ford et al (USA)24 | Parallel group | Community (multicentre, n=2) | A: Enhanced recruitment letter, phone screening by an African American interviewer, baseline questionnaire by mail, reminder calls/mailings for baseline info and consent | Standard recruitment letter, phone screening by an African American/Caucasian interviewer, baseline questionnaire by mail, reminder calls/mailings for return of baseline info and consent | African American men aged 55–74, eligible for a prostate, lung and colorectal cancer screening trial | 78/3079 (2.5%) | 95/3297 (2.9%) | B | Between-group difference was statistically significant (p<0.01) |
| B: Enhanced recruitment letter, phone screening by an African American interviewer, baseline questionnaire by phone, reminder calls/mailings for consent form | 87/3075 (2.8%) | ||||||||
| C: Enhanced recruitment letter, phone screening by an African American interviewer, reminder for project session held at church, baseline questionnaire at church session | 116/2949 (3.9%) | ||||||||
| Fowell et al (UK)25 | Clustered cross-over | Secondary care (multicentre, n=2) | Cluster randomisation | Zelen's design (only those randomised to intervention arm asked for consent) | Cancer inpatients receiving palliative care and starting on a syringe driver | 6/24 (25%) | 0/29 (0%) | C | Considered the effect of trial design on potential recruitment rate; aimed to explore the feasibility of the two designs for studies of dying patients; between-group difference was statistically significant (p=0.02) |
| Free et al (UK)26 | Parallel group | Community (multicentre, n=2) | A: A letter containing study and consent information, and a £5 note | Normal trial procedures (letter and patient information sheet) | Members of the public who are aged ≥16, are daily smokers and willing to quit in the next month | 13/246 (5.3%) | 1/245 (0.4%) | A | Evaluated interventions in separate trials; between-groups differences were statistically significant for both the financial incentive (OR 4.9; 95% CI 2.0 to 7.7) and text messages (OR 4.2; 95% CI 2.2 to 6.1) |
| B: Four text messages over 1 week containing quotes from existing participants | Normal trial procedures (letter and patient information sheet) | 17/405 (4.2%) | 0/406 (0%) | ||||||
| Freer et al (UK)27 | Parallel group | Tertiary neonatal intensive care unit | A: Five page US version of a study information leaflet (inc. more detail on study process, risks, benefits and patient rights) plus standard verbal explanation | US version of an information leaflet without verbal explanation | Parents of immature infant(s) admitted to the NICU but not requiring intensive care | 5/9 (56%) | 3/9 (33%) | B | Considered the impact of information on parents’ understanding of a research study and the validity of their consent to participation in a hypothetical trial; no information on statistical significance given |
| B: Less detailed single sheet UK version of a study information leaflet plus standard verbal explanation | UK version of an information leaflet without verbal explanation | 5/9 (56%) | 4/10 (40%) | ||||||
| Fureman et al (USA)28 | Parallel group | Existing trial (university based) | Enhanced video on an HIV vaccine trial plus a 1 h pamphlet presentation (5 min pre-test, 26 min of video, 10 min to review pamphlet, RA initiated Q&A session, post-test questionnaire, survey at 1 month | Standard half hour pamphlet-only presentation (5 min pre-test, 10 min to review a trial info pamphlet, RA initiated Q&A session, post-test questionnaire, survey at 1 month | Participants in the Risk Assessment Project (injection drug users) | 1.84 (post-test 1); 1.69 (post-test 2) | 1.70 (post-test 1); 1.50 (post-test 2) | C | Studied recruitment to a hypothetical trial (targeted 98 individuals for intervention, 88 for comparator); results provided as mean willingness scores; between-group difference was not statistically significant (p>0.1) |
| Graham et al (USA)29 | Parallel group | Health Maintenance Organisation (multicentre) | A: Electronic questionnaire on hazardous drinking and willingness to participate in lifestyle intervention | Standard self-complete paper questionnaire | Patients aged ≥18 attending the HMO with an acute injury | 69/151 (45.7%) | 76/141 (53.9%) | C | Considered different methods of screening, which included willingness to participate in a hypothetical trial; between-group difference was statistically significant (p=0.001) |
| B: Oral questionnaire read aloud to patients in the clinic, potential answers printed on cards and patients asked to point | 42/78 (53.8%) | ||||||||
| Halpern et al (USA)30 | Within-subject design | Secondary care | A: Variation in trial information on (1) the percentage of previous patients experiencing an adverse effect from the study drug (10%, 20%, 30%) and (2) payment participants would receive ($100, $1000, $2000) | Not applicable | Patients with mild to moderate hypertension attending an outpatient clinic | Unclear | Not applicable | C | Assessed willingness to take part in hypothetical studies by risk and reward; did not provide recruitment rates (126 participants); there was a statistically significant increase in willingness to participate as risk of adverse effects reduced (p<0.001), payment level rose (p<0.001), and the risk of being assigned to placebo decreased (p=0.02) |
| B: Variation in trial information on (1) the percentage of patients who would be assigned to placebo (10%, 30%, 50%) and (2) the payment level (payment in range typically offered to participants in phase 3 trials of antihypertensive drugs) | Unclear | ||||||||
| Harris et al (UK)31 | Factorial | Community | A: Personal recruitment letter and info plus telephone reminder (up to four) plus questionnaire on physical activity | Not applicable | Households of older people aged ≥65, able to walk outside and registered with one GP practice | 69/140 (49.3%) | Not applicable | A | Between-group difference was statistically significant for telephone reminders (OR 1.5; 95% CI 1.0 to 2.3), but not for the inclusion of a questionnaire (OR 0.9; 95% CI 0.6 to 1.3) |
| B: Personal recruitment letter and info plus telephone reminder (up to four) | 65/140 (46.4%) | ||||||||
| C: Personal recruitment letter and info plus questionnaire on physical activity | 47/140 (33.6%) | ||||||||
| D: Personal recruitment letter and info only | 59/140 (42.1%) | ||||||||
| Hemminki et al (Estonia)32 | Parallel group | Local clinics (multicentre) | Non-blinded allocation comparing active HRT treatment with no treatment | Traditional blinded allocation comparing active HRT treatment with placebo | Postmenopausal women aged 50–64 | 1027/2159 (47.6%) | 796/2136 (37.3%) | A | Between-group difference was statistically significant (p<0.001) |
| Hutchison et al (UK)33 | Parallel group | Secondary care | Video giving generic and site-specific trial info with a focus on randomisation, pictures of patients receiving care and a voiceover discussing uncertainty plus standard practice | Standard practice of clinician from tumour site team discussing trial and administering trial specific info sheet and consent form; at next visit patient sees a clinician from the same team to decide on treatment and whether it will be part of a trial | Patients with colorectal, breast or lung cancer, and eligible for a cancer treatment trial | 62/86 (72.1%) | 66/87 (75.9%) | A | Considered recruitment to a range of cancer trials; between-group difference was not statistically significant (p=0.661) |
| Ives et al (UK)34 | Parallel group | Secondary care | Standard trial information plus booklet entitled, “Clinical Trials in HIV and AIDS: Information for people who are thinking about joining a trial” | Standard trial information (information sheet specific to proposed trial plus discussion with trial doctor and research nurse) | Patients attending an HIV hospital clinic | 15/23 (65.2%) | 11/27 (40.7%) | C | Considered recruitment of patients eligible for participation in eight trials being carried out at the participating institution; no information on statistical significance given |
| Jeste et al (USA)35 | Parallel group | Secondary care | Multimedia consent with DVD presenting key information from consent form, including simultaneous narrative explanation; researcher also present to answer questions | Routine consent procedure plus 10 min control DVD giving general information about research; researcher also present to answer questions | Outpatients aged >40 with schizophrenia, and healthy comparison subjects | 41/62 (66.1%) patients with schizophrenia; 23/31 (74.2%) healthy comparisons | 44/66 (67.2%) patients with schizophrenia; 22/29 (75.9%) healthy comparisons | B | Studied agreement to participate in a hypothetical trial; between-group differences were not statistically significant (no p value provided) |
| Karunaratne et al (Australia)36 | Parallel group | Secondary care | Computer-based, interactive presentation of study information inc. diagrams, video clips, hyperlinks, quiz pages | Conventional paper-based study information | Patients aged 18–70 attending an outpatient diabetic clinic | 23/30 (76.7%) | 17/30 (56.7%) | C | Considered participant understanding of consent materials, including interest in participating in a hypothetical trial; between-group difference was statistically significant (p=0.01) |
| Kendrick et al (UK)37 | Parallel group | Primary care (multicentre) | Mailed invitation to participate in an injury prevention trial, including a home safety questionnaire | Mailed invitation to participate excluding home safety questionnaire | Families with children aged<5 years, living in deprived areas | 217/1203 (18.0%) | 157/1190 (13.2%) | A | Between-group difference was statistically significant (p=0.001) |
| Kerr et al (UK)38 | Parallel group | Further education colleges (multicentre, n=5) | A: Leaflet describing a trial of two treatments for arthritis, where A and B are described as standard treatments | Not applicable | Students aged ≥18 enrolled on further education/leisure courses | 24/29 (82.8%) | Not applicable | C | Studied willingness to participate in a hypothetical trial; did not provide recruitment rates (130 participants); between-group difference was statistically significant (p<0.001), with those who had a preference for a standard treatment—available outside of the trial—less willing to participate than those with no preference |
| B: Leaflet describing a trial of two treatments for arthritis, where A is described as new treatment and B as standard treatment | 10/17 (58.8%) | ||||||||
| C: Leaflet describing a trial of two treatments for arthritis, where B is described as new treatment and A as standard treatment | 13/16 (81.3%) | ||||||||
| D: Leaflet describing a trial of two treatments for back pain, where A and B are described as standard treatments | 26/31 (83.9%) | ||||||||
| E: Leaflet describing a trial of two treatments for back pain, where A is described as new treatment and B as standard treatment | 10/15 (66.7%) | ||||||||
| F: Leaflet describing a trial of two treatments for back pain, where B is described as new treatment and A as standard treatment | 10/16 (62.5%) | ||||||||
| Kimmick et al (USA)39 | Cluster | Secondary care and academic institutions (multicentre, n=126) | Educational intervention of standard info plus an educational symposium, geriatric oncology educational materials, monthly mailings and emails for 1 year, lists of available protocols for use on patient charts, case discussion seminar | Standard information of periodic notification of all existing CALGB (Cancer and Leukaemia Group B) trials by the CALGB Central Office, and CALGB web site access | Practitioners and researchers from CALGB institutions | 36% in year 1; 31% in year 2 | 32% in year 1; 31% in year 2 | C | Considered recruitment of older people to existing CALGB treatment trials for a range of cancers; between-group difference was not statistically significant at year 1 (p=0.35) or at year 2 (p=0.83) |
| Larkey et al (USA)40 | Parallel group | Existing trial sites (multicentre, n=2) | A: Hispanic lay advocates; attended 6 h long training sessions, five quarterly meetings and received brochures with interest cards to distribute to other women | Anglo women controls, received quarterly ‘phone calls and brochures with interest cards to distribute to other women | Participants in the Women's Health Initiative trial | 13/31 referrals (41.9%) | 2/19 referrals (10.5%) | B | Determined whether Hispanic women already enrolled in a study and trained as lay advocates would refer/enrol more participants than untrained Hispanic women and Anglo controls; between-group difference was statistically significant (p<0.01) |
| B: Hispanic women controls, received quarterly ‘phone calls and brochures with interest cards to distribute to other women | 0/3 referrals (0.0%) | ||||||||
| Liénard et al (France)41 | Cluster | Secondary care (multicentre, n=135) | Site visits including an initiation visit to review trial protocol, inclusion/exclusion criteria, safety, randomisation, etc plus ongoing review visits | No site visits (unless requested) | Centres recruiting to an RCT for breast cancer | 302 | 271 | A | No denominator data provided; between-group difference was not statistically significant (no p value provided) |
| Litchfield et al (UK)42 | Cluster | Primary care (multicentre, n=28) | Internet-based collection of trial data | Paper-based collection of trial data | 28 participating GP practices | 45/52 (86.5%) | 28/28 (100%) | B | Considered efficiency and ease of use of internet versus conventional paper-based data capture, and looked at recruitment incidentally; between-group difference was statistically significant (p=0.04) |
| Llewellyn-Thomas et al (Canada)43 | Parallel group | Secondary care | A: Booklet with negatively framed intervention about treatment side-effects and survival | Booklet with neutrally framed intervention about treatment side-effects and survival | Colorectal cancer patients attending cancer hospital outpatients | 20/30 (66.7%) | 23/30 (76.7%) | B | Determined the impact of probabilistic info on entry to a hypothetical trial; between-group difference was not statistically significant (p>0.40) |
| B: Booklet with positively framed intervention about treatment side-effects and survival | 18/30 (60.0%) | ||||||||
| Llewellyn-Thomas et al (Canada)44 | Parallel group | Secondary care | Searchable computerised info on imaginary trial, including purpose, description of treatment arm and randomisation, possible benefits, side-effects, patients’ rights | Tape-recorded info on imaginary trial, including purpose, description of treatment arm and randomisation, possible benefits, side-effects, patients’ rights | Patients attending the outpatient department of a cancer hospital | 31/50 (62.0%) | 21/50 (42.0%) | B | Studied recruitment to a hypothetical trial; between-group difference was statistically significant (p<0.05, unadjusted) |
| Mandelblatt et al (USA)45 | Parallel group | Community (multicentre, n=3) | 5–10 min educational counselling session about the trial delivered by non-physician study staff (inc benefits and risk of participation and need for minority participation) plus an informational brochure | Informational brochure only | Spanish speaking women who were eligible for a trial on women at high risk of breast cancer | 178/232 (76.7%) general intent;118/232 (50.9%) if mild side-effects mentioned;108/232 (46.6%) if uterine cancer mentioned | 147/218 (67.4%) general intent;118/218 (54.1%) if mild side-effects mentioned;97/218 (44.5%) if uterine cancer mentioned | C | Results relate to intention to participate (‘might, probably or definitely would’); between-group difference was statistically significant for general intention to participate (p=0.03) |
| Miller et al (USA)46 | Parallel group | Secondary care, primary care and community | Eligibility screening and recruitment by a senior investigator | Eligibility screening and recruitment by a Research Assistant | Patients aged 18–75, eligible for participation in two chronic depression treatment trials | 28/162 (17.3%) | 22/185 (11.9%) | C | Considered the relationship between interviewer experience and positive predictive value and cost of telephone screening, and looked at recruitment incidentally; between-group difference was not statistically significant (p=0.30) |
| Monaghan et al (Worldwide)47 | Cluster | Existing trial sites (multi-centre, n=167) | Additional communication—usual plus frequent emails, regular personalised mail-outs of league tables/graphs of performance against other sites, certificates of achievement for recruitment/other study items (1/month) | Usual communication (provided via the regional centre) plus occasional direct communications from the co-ordinating centre in the form of generic newsletters, emails and faxes | Clinical sites in 19 countries recruiting to a diabetes and vascular disease treatment trial | 37.5 (27.0–51.5) | 37.0 (21.0–54.5) | A | Result provided as median number of participants recruited; between-group difference was not statistically significant (p=0.68) |
| Myles et al (Australia)48 | Parallel group | Secondary care | A: Prerandomised to experimental drug and asked to provide consent; if no consent, standard treatment given | Standard randomisation method (equal chance of either drug) | Inpatients aged ≥18, scheduled for elective surgery | 90/169 (53.3%) | 84/151 (55.6%) | B | Considered recruitment to a hypothetical trial; between-group difference was not statistically significant (p=0.66) |
| B: Prerandomised to standard drug and asked to provide consent; if no consent, experimental treatment given | 79/149 (53.0%) | ||||||||
| C: Told that physician thinks experimental drug superior, if consent given, has 70% chance of receiving this; if no consent, standard treatment given | 91/150 (60.7%) | ||||||||
| D: Allowed to increase or decrease chance of receiving experimental drug if consent given, and if no preference, 50% chance of receiving it; if no consent, standard treatment given | 85/150 (56.7%) | ||||||||
| Nystuen and Hagen (Norway)49 | Parallel group | Community (multicentre, n=6) | Written invitation to participate in a community-based trial followed by a ‘phone reminder if no response within 2 weeks; guide used for discussion | Written invitation to participate in a community-based trial followed by no reminder if no response within 2 weeks | Sick-listed employees attending a participating social security office | 31/256 (12.1%) | 11/242 (4.5%) | A | Between-group difference was statistically significant (p=0.003) |
| Perrone et al (Italy)50 | Parallel group | Community | A: randomised consent to new treatment; if no consent given standard treatment | On consent to participate, standard or new treatment assigned at random; if no consent, given standard treatment | Members of the general public aged 16–80, attending a scientific exhibition | 997/1151 (86.6%) | 836/985 (84.9%) | C | Studied recruitment to a hypothetical trial; between-group difference was significant for both the single (p=0.08) and double consent scenarios (p<0.0001) |
| B: randomised consent to standard treatment; if no consent given new treatment | 246/474 (51.9%) | ||||||||
| C: if consents to participate, standard or new treatment assigned at random; if no consent, can choose standard or new treatment | 482/607 (79.4%) | ||||||||
| Pighills et al (UK)51 | Parallel group | Primary care (multicentre) | A: Newspaper article about the trial included with recruitment materials | Usual recruitment materials only | Men and women aged ≥70 who had at least one fall in the previous 12 months | 73/2243 (3.3%) | 71/2245 (3.2%) | B | Evaluated interventions in separate trials; between-group differences were not statistically significant (p=0.80; p=0.62) |
| B: Inclusion of a more ‘upbeat’ newspaper article about the trial | Inclusion of the Intervention A newspaper article | 57/1374 (4.1%) | 54/1371 (3.9%) | ||||||
| Simel and Feussner (USA)52 | Parallel group | Secondary care | Consent form including a statement that the new treatment may work twice as fast as usual treatment | Consent form including a statement that the new treatment may work half as fast as usual treatment | Patients attending an ambulatory care clinic | 35/52 (67.3) | 20/48 (41.7%) | B | Considered recruitment to a hypothetical trial; between-group difference was statistically significant (p<0.01) |
| Simes et al (Australia)53 | Parallel group | Secondary care | Individual approach to consent—patients given info about aims, expected results, potential toxicities of treatment; details of treatment left to discretion of consultant; patients given opportunity to ask questions, verbal consent obtained | Total disclosure approach—patients fully informed about all trial aspects by consultant: patients given opportunity to ask questions, also given a consent form outlining the info; this was kept overnight and written consent obtained next day | Patients attending an oncology unit | 27/29 (93.1%) | 23/28 (82.1%) | A | Considered recruitment of patients eligible for 16 trials being carried out at the participating institution; between-group difference was statistically significant (p=0.01) |
| Treschan et al (Austria)54 | Parallel group | Secondary care | A: Info on study of wound healing said to have no risk but involving additional procedures described as provoking considerable pain and discomfort | Info on study of wound healing described as posing essentially no risk and producing no significant pain | Patients aged 19–80, and scheduled for minor surgery with general anaesthesia | 18/51 (35%) | 30/47 (64%) | B | Studied willingness to participate in a hypothetical trial, although patients were not aware of this until after the decision to take part; between-group difference was statistically significant (p<0.001) |
| B: Info on study of wound healing said to have no pain but involving additional procedures described as inducing risk of injury | 13/50 (26%) | ||||||||
| Trevena et al (Australia)55 | Sequential start | Primary care | Opt-out recruitment; letter from doctor advising that practice taking part in screening trial; would be contacted unless practice advised to withhold contact details | Opt-in recruitment; letter from doctor advising that practice taking part in screening trial; would only be contacted if contact details returned | Patients aged 50–74 eligible for a colorectal cancer screening trial | 40/60 (66.7%) | 44/92 (47.8%) | A | Compared the effect of opt-in requirements in new privacy laws with an opt-out approach that was previously permissible; no information on statistical significance given |
| Wadland et al (USA)56 | Parallel group | Primary care | Consent form read out to potential participants by study co-ordinator | Consent form read by potential participants | Current smokers aged ≥18 | 27/51 (53%) | 25/53 (47%) | C | Smoking cessation study carried out in two practices, with the intervention evaluated in one; between-group differences were not statistically significant (no p value provided) |
| Weinfurt et al (USA)57 | Parallel group | Secondary care | A: Consent documents containing a disclosure indicating that the clinic received per capita payments covering the costs of the research (including investigator's salary) | Consent documents containing no financial disclosure | Patients of a cardiovascular outpatient clinic aged ≥18, and diagnosed with coronary artery disease | 3.51 (SD 1.30) | 3.50 (SD 1.29) | C | Studied willingness to participate in a hypothetical trial; did not provide recruitment rates (470 participants); results provided as mean willingness scores; between-group difference was statistically significant (p=0.02); patients in the equity group were also less willing to participate than those in the per capita (p=0.01) and no disclosure groups (p=0.03) |
| B: Consent documents containing a disclosure describing an investment by the investigator in the company sponsoring the research (‘equity’) | 3.20 (SD 1.32) | ||||||||
| Weinfurt et al (USA)58 | Parallel group | Community | A: Info inc a general disclosure that the investigator may gain financially from the study plus a statement that ethics committee does not think this affects patient safety or study quality | Not applicable | Aged ≥18 with asthma or diabetes and a member of a panel of adults who agreed to be contacted about research opportunities | 3.28 (SD 0.04) | Not applicable | C | Studied willingness to participate in a hypothetical trial; did not provide recruitment rates (3623 participants); results provided as mean willingness scores; between-group difference was statistically significant (p<0.001) |
| B: Info inc a disclosure that the drug company pays running costs to the investigator plus a statement that ethics committee does not think this affects safety or quality | 3.46 (SD 0.04) | ||||||||
| C: Info inc a disclosure that the drug company pays monies out with the study to the investigator plus a statement that ethics committee does not think this affects safety or quality | 3.22 (SD 0.04) | ||||||||
| D: Info inc a disclosure that the investigator has an investment in the drug company plus a statement that ethics committee does not think this affects safety or quality | 3.16 (SD 0.04) | ||||||||
| E: Info inc a disclosure that the investigator's institution has an investment in the drug company plus a statement that ethics committee does not think this affects safety or quality | 3.28 (SD 0.04) | ||||||||
| Welton et al (UK)59 | Parallel group | Primary care (multicentre, n=10) | Verbal info about a trial of HRT, comparing oestrogen only, with combined oestrogen and progestogen, with placebo | Verbal info about a trial of HRT, comparing oestrogen only with combined oestrogen and progestogen | Women aged 45–64 who had not had a hysterectomy | 65/218 (29.8%) | 85/218 (39.0%) | C | Considered willingness to take part in a hypothetical trial; between-group difference was not statistically significant (p=0.06) |
| Weston et al (Canada)60 | Parallel group | Secondary care (multicentre) | Written study information followed by viewing of Term Prelabour Rupture of the Membranes (Term PROM) video | Written study information only | Women attending for antenatal visits | 26/42 (61.9%) initially; 23/41 (56.1%) at 2–4 weeks | 17/48 (35.4%) initially; 17/44 (38.6%) at 2–4 weeks | B | Between-group difference was statistically significant (p=0.01) |
*Risk of bias: A, low; B, moderate; C, high.
†Includes difference in outcomes as reported by the authors.
RCT, randomised controlled trial.