Table 2. Details of studies including: methods, total number of participants, GPs, and practices recruited, setting and participant population, intervention categories and comparisons.

Study	Methods	Total number of participants (pts) /GPs/practices recruited	Cost per recruit	Setting and participant population	Intervention categories	Comparisons
Andersen 2010	Yield study	187 pts	Not reported	Primary care, Norway. Adults aged 65 years or older, with a Mini-Mental State Examination (MMSE) sum score of ≥10 and ≤30 points	Face to face recruitment initiatives Postal invitations and responses	Compared the use of mailed invitation letters with face to face recruitment through routine GP practice appointments
Barrera 2014	Yield study	2575 pts	Not reported	Online, USA. Pregnant adult women aged 18 years or older	Language adaptations	Compared the use of Google AdWords in Spanish and English
Beauharnais 2012	Before and after study	31 pts	Not reported	Secondary care, USA. Patients with an HbA1C value of >7.5% who had been admitted to acute general medical or surgical units for reasons other than hyperglycaemia	Trial awareness strategies aimed at the recruiter	Compared use of an automated pre-screening algorithm with manual chart review
Bell-Syer 2000	Cohort study	187 pts	Not reported	Primary care, UK. Adults aged 18 to 60 who had experienced low back pain for no more than six months	Face to face recruitment initiatives Postal invitations and responses	Compared the use of computerised, postal referral, with manual, personal participant referral methods
Bhar 2013	Yield study	33 pts	Not reported for referral from primary care physicians or referral of inpatients. Referral of outpatients and patients at a veterans’ affairs medical centre: USD$166 and USD$44, respectively Mailing from primary care patient lists: USD$636	Primary and secondary care, USA. Adult men aged 60 or older, with a scored greater than 0 on the fourth item on the Scale for Suicide Ideation	Face to face recruitment initiatives Postal invitations and responses	Compared recruitment via referrals from primary care physicians, psychiatry residents (outpatients), an inpatient psychiatric unit, and a Veterans Affairs medical centre, and mailing from primary care patient lists
Brealey 2007	Yield study	553 pts	Not reported	Primary care, UK. Aged between 18 and 55 years inclusive, and their GP was considering referral to an orthopaedic specialist for suspected internal derangement of the knee	Randomisation methods	Compared the use of postal and telephone randomisation methods (this was deemed to be a recruitment method as delays to the start of the recruitment period were the driving force behind this change to randomisation methods).
Carr 2010	Yield study	69 pts	Community outreach event: USD$55.18 The total cost of the education event was USD$3,372.80; no participants were recruited over the subsequent four-month period	Primary care and within the community, USA. Cognitively normal and cognitively-impaired elderly people	Trial awareness strategies aimed at the recruitee Trial awareness strategies aimed at the recruiter	Compared a community outreach event aiming to improve public awareness of the trial, with a continuing medical education event aiming to improve trial knowledge among community physicians
Carter 2015	Yield study	120 pts	Face to face recruitment initiatives: GBP£105 Postal methods: GBP£15 Traditional awareness strategies: GBP£55	Primary and secondary care, and within the community, UK. Multiple sclerosis patients between 18 and 65 years of age	Face to face recruitment initiatives Postal invitations and responses Trial awareness strategies aimed at the recruitee	Compared consultant referral at MS outpatient clinics, with mail outs, and traditional trial awareness strategies
Colwell 2012	Cohort study	54 practices	Not reported	Primary care, UK. Paper reports recruitment of GP practices who were then charged with recruiting participants with type II diabetes mellitus	Trial awareness strategies aimed at the recruiter	Investigated the effect of viral marketing techniques (primer postcard and flyer) sent before invitation packs
Elley 2007	Cohort study	312 pts	Not reported	Primary care, New Zealand. Adults aged 75 of over (over 55 years for Maori and Pacific people) that had fallen in the last 12 months	Face to face recruitment initiatives Postal invitations and responses	Compared recruitment conducted in practice waiting rooms with mailed invitation letters
Embi 2005	Before and after study	59 pts	Not reported	Secondary care, USA. The paper reports on endocrinologists and general internists (main campus and community health centres) who were recruiting patients with type 2 diabetes	Trial awareness strategies aimed at the recruiter	Compared a clinical trial alert system on the electronic health record of eligible patients with traditional recruitment methods only
Funk 2012	Yield study	469 pts	Not reported	Primary and secondary care, USA. Adults over the age of 30 with a body mass index between 30 and 50 kg/m 2	Postal invitations and responses	Compared the method of response (telephone versus website) after potential participants were mailed a brochure about the trial
Gill 2001	Yield study	188 pts	Face to face initiatives: USD$868 Postal methods: USD$764	Primary care, USA. Adults aged 75 or older, who were physically frail	Face to face recruitment initiatives Postal invitations and responses	Compared face to face screening in primary care practices with face to face screening in the potential participant’s home
Johnson 2015	Yield study	89 pts	Not reported	Primary and secondary care, and within the community, USA. Adults with veteran status, a BMI ≥25kg/m 2, and a current prescription for insulin or oral medications to control blood glucose	Face to face recruitment initiatives Postal invitations and responses Trial awareness strategies aimed at the recruitee	Compared the method of response (telephone versus postcard) by potential participants after they were mailed a brochure about the trial, with staff contacting potential participants by telephone after they were mailed a brochure about the trial, as well as non-targeted flyers and clinician referrals
Lamont 2010	Yield study	2708 pts	Not reported	Primary and secondary care, and within academic centres and community affiliates, USA. Lung cancer patients	Face to face recruitment initiatives	Compared recruitment by setting; academic, community and Veterans Health Administration sites.
Sawhney 2014	Before and after study	212 pts	Not reported	Secondary care, UK. Defibrillator patients attending the cardiac arrhythmia clinic at St Bartholomew’s Hospital	Trial awareness strategies aimed at the recruitee	Compared telephone contact with participants that had been mailed information about the trial prior to their clinic appointment
Shah 2014	Cohort study	150 GPs	Not reported	Primary care, Australia. Paper reports recruitment of general practitioners by the research team	Face to face recruitment initiatives	Compared the effect of different individuals approaching general practitioners (staff from independent GP research organisation, Chief Investigator, project staff from the University)
Treweek 2010	Yield study	29 pts	Not reported	Primary Care, UK. Cohort 1: aged between 35 and 80 years, with an HbA1C value of >7% and <10%, with no prescription for any diabetes therapy in previous six months. Cohort 2: aged ≥35 and <80, with an HbA1C value of >7% and ≤9%, with a prescription for metformin within the last six months	Face to face recruitment initiatives Postal invitations and responses Trial awareness strategies aimed at the recruiter	Compared SARMA software (screening software that flags eligible patients to staff) with referral during clinic appointments, and a research nurse approaching patients at routine clinic appointments
Park 2007	Yield study	442 pts	Not reported	Secondary care and within the community, USA. Pregnant women aged 18 or older, that had smoked ≥1 cigarette in the past seven days and were up to 26 weeks of gestation	Use of networks and databases	Compared centralised recruitment efforts (i.e. existing identification and referral systems) with a de-centralised practice-based recruitment strategy (i.e. referral systems built specifically for the study)
Weng 2010	Yield study	44 pts	Not reported	Primary and secondary care, USA. Adults aged 50 or older with type 2 diabetes mellitus, an A1C measurement of between 6.5 and 8%, and pre- existing ischaemic vascular disease	Use of networks and databases	Compared a clinical data warehouse from a large medical centre, with use of a registry to identify potential participants