Table 1.

Details of included studies

Study ID	Aims of study	Study sample	Study topic	Study design	Total number of subjects in study (N)	Control (n)	Intervention (n)	Country
Akl et al., 2011 [41]	Assess the effect of 1) tracking responses and 2) day of mailing (Monday vs Friday) on physician survey response rate	Directors of Family Medicine residency programs (ie GPs)	Training of residents in implementation of clinical guidelines	Two by two factorial randomized design	456	No tracking n = 228, Monday mailing n = 228	Tracking n = 228, Friday mailing n = 228	USA
Asch et al., 1998 [26]	To evaluate the effect of incentive size by providing physicians either a $5 bill or a $2 bill.	Primary care physicians identified from the American Medical Association Physician Master File	Attitudes about cost containment in cancer screening.	RCT	1000	$2 cash incentive received in initial mailing n = 500	$5 cash incentive received in initial mailing n = 500	USA
Baron et al., 2001 [29]	To evaluate the cost effectiveness of a lottery on physicians response rates to a mail survey.	Family Doctors identified from membership list of the Quebec Federation of GPs	The determinants of influenza immunization among family physicians in Quebec.	RCT	1000	No lottery n = 500	Lottery n = 500	Canada
Bonevskiet al., 2011 [40]	To examine the efficacy of two strategies for improving general practitioner response to a survey and a secondary aim was to assess GPs self reported preferred mode of survey administration.	GPs practising in NSW selected from the Australasian Medical Publishing Company database.	The knowledge, attitudes and practices of GPs around vitamin D.	RCT	334 (Cover letter trial), 1166 (Telephone reminder trial)	Standard cover letter N = 167, No telephone reminder n = 576	Standard letter plus local division of general practice cover letter n = 167, Telephone reminder n = 590	Australia
Deehan et al., 1997 [11]	To explore the effects of financial and non-financial inducements on response rates to increase the overall response rate.	A random sample of all GP’s in England and Wales.	Survey on GP’s work and attitudes with alcohol misusing patients.	Five arm parallel trial design with randomization	3584	No inducement n = 1188	£5 charity donation n = 607, £10 charity donation n = 578, £5cash payment n = 613, £10 cash payment n = 598, (Total for all interventions n = 2396)	UK
Drummond et al., 2008 [34]	To investigate the effect of two low cost interventions (pre-contact and questionnaire order) on response to a primary care physician postal survey	Primary care physicians working in Ireland identified from various sources.	A national survey assessing views and practices of physicians regarding prostate specific antigen (PSA) testing.	Two by two factorial randomized design	1599	No pre-contact n = 743, Version 2 survey (Topic specific questions first) n = 744	Pre-contact n = 715, Version 1 survey (general questions first) n = 714	Ireland
Everett et al., 1997 [28]	To examine the effectiveness of $1 incentive on response rates	Family Physicians	Firearm-safety counseling beliefs	RCT	600	No incentive n=300	$1 bill n=300	USA
Gattellari et al., 2012 [13]	Assess effectiveness of two response-aiding strategies in a postal survey	GPs known to be in current practice	Management of nonvalvular atrial fibrillation	Two by two factorial randomized control trial	1000	Mail prompt n = 500, Coloured seal without text n = 500	Fax prompt n = 500, Coloured seal + text n = 500	Australia
Gupta et al., 1997 [39]	To determine the effectiveness of a telephone prompt by a medical researcher compared to a nonmedical research assistant in improving survey response rate of GP’s, and to compare personnel costs.	A national random sample of Australian GPs	A national survey assessing GPs views of clinical practice guidelines	RCT	404	Telephone prompt by a medical researcher n = 202	Telephone prompt by experienced nonmedical research assistant n = 202	Australia
Hocking et al., 2006 [35]	To compare GP response to a telephone interview with response to a postal survey with three reminders.	A random sample of Victorian GPs	Survey to assess knowledge and diagnostic and management practices of genital chlamydia infection.	RCT	867	Postal survey n = 451	Telephone interview n = 416	Australia
James et al., 2011 [27]	To study the effects of payment timing, form of payment and requiring a social security number (SSN) on survey response rates.	Practising US physicians ages 65 and under representing all specialties (including primary care), selected from the AMA Physician Masterfile	Survey on ethical and moral beliefs.	Four arm parallel design with randomization	443	Promised $US25 check requiring SSN n = 102	Immediate $US25 cash n = 129, Immediate $US25 check n = 97, Promised $US25 check not requiring SSN n = 115	USA
McLaren and Shelley 2000 [30]	To compare effect of a primer telephone call and postcard on GP response rate; and to compare the effect of informing GPs about a prize for participating in survey compared to not informing GPs of the prize.	Victorian GPs	Management issues surrounding early pregnancy bleeding and miscarriage	Two by two factorial design with randomization	621	Telephone n=305 No prize notification N=310	Postcard n=316Prize notification n=311	Australia
Maheux et al., 1989 [42]	To determine the response rates of Quebec physicians by sending a handwritten thank you letter and by sending a more personalized mailout package.	Quebec Physicians	To determine the level of physicians support for a number of patient care issues.	RCT	Second mailing N = 356, Third mailing N = 253	No handwritten postscript n = 186, Non-personalised mailout n = 127	Handwritten postscript n = 170, Personalised mailout n = 126	Canada
Olivarius and Andreasen, 1995 [43]	To test a possible day the week effect on doctors response rate to a postal questionnaire.	GPs	A nationwide survey on doctors’ attitude on the relative importance of general practice and the specialties in the treatment of general diseases and diseases commonly regarded as belonging to the specialties.	RCT	200	Dispatch of survey on Thursday (for receipt before weekend) n = 98	Dispatch of survey on Saturday (for receipt after weekend) n = 102	Denmark
Pedrana et al., 2008 [44]	To compare response rates to postal surveys sent by normal post and registered mail and to assess the cost implications of the two mailing methods.	General practitioners in Victoria.	To assess antenatal screening practices in Australia	RCT	1550	Normal mail n = 775	Registered mail n = 775	Australia
Pirotta et al., 1999 [38]	To measure the effect of a primer postcard to improve mailed survey response rates.	Victorian GPs who had at least 1500 consultations in 1995-96	General Practitioners attitudes to complementary therapies.	RCT	800	No primer postcard n = 400	Primer postcard n = 400	Australia
Pit et al., 2013 [25]	To assess the effectiveness of small non-conditional non-financial incentive (ie attractive pen) on survey response rates	Practicing GPs in Northern Rivers region of NSW	How to improve sustainable employment of ageing GPs in rural Australia	RCT	125	No pen incentive n = 62	Pen incentive n = 63	Australia
Robertson et al., 2005 [31]	To test the effect of a $AUD2 scratch lottery ticket on response rates	A random sample GP’s and specialists from the medical directory of Australia.	To explore the uptake of 19 new drugs into the clinical practices of Australian GPs and specialists.	RCT	464	No lottery n = 232	AUD$2 scratch lottery n = 232	Australia
Scott et al., 2011[24]	To compare effects and costs of three different modes of survey administration in a national survey of Doctors	A stratified random sample of doctors undertaking clinical practice from a national directory of all doctors in Australia. Stratification was by doctor type and rural/remote category.	Study of the dynamics of the medical labour market in Australia, focusing on workforce participation and its determinants among Australian doctors.	3-arm parallel trial design with randomisation	1091	Online survey, followed by reminder letter with login details n = 369	Sequential mixed mode -online survey, followed by reminder letter with paper survey n = 388, Simultaneous mixed mode -paper survey and login details sent together, with reminder letter with login details n = 334	Australia
Seguin et al., 2004 [37]	To compare email with regular mail for conducting surveys of family physicians.	A random sample of physicians listed in the college of family physicians of Canada’s database who had an email address	Survey on use of sildenafil citrate (Viagra)	RCT	2397	Survey delivered by post to the physicians without email n = 800	Survey delivered by email n = 798, Survey delivered by post to the physicians with e mail n = 799	Canada
Shosteck and Fairweather, 1979 [36]	Comparison of mail and personal administration of questionnaire among physicians.	Office-based primary care physicians who were in active practice within the States of Washington DC and Maryland, and treating upper respiratory or lower urinary tract infections selected from the AMA database.	Physician antibiotic prescription practices.	RCT	543	Mail technique n = 296	Personal interview technique n = 247	USA
Thomson et al., 2004 [32]	To maximise the response to a postal questionnaire and to test the most effective form of incentive.	Practicing GP’s selected from the Lothian Primary Care NHS Trust database.	GP’s attitudes to the management of ingrowing toenails.	RCT	568	Lottery of one chance to win six bottles of champagne n = 286	Lottery of six chances to win one bottle of champagne n = 282	UK
Ward et al., 1998 [33]	To evaluate response aiding strategies feasible in large surveys	Randomly selected sample of general practitioners	Cancer screening	4-arm parallel trial design with randomisation	1550	-	Doctor advance phone prompt: n = 249, Pen prompt: n = 261, Letter prompt: n = 260, Non-doctor advance phone prompt: n = 501	Australia