Table 1.

Characteristics of included studies (N=15)

Study	Study aim	Study design	Material	Country	Inclusion period	Area of interests	Results	Conclusion
Clarke M, Alderson P, Chalmers I. (2002) [27]	To assess whether RCTs in 5 general medical journals discuss new results in light of available evidence.	Cross-sectional	RCTs published in Annals of Int Med, BMJ, JAMA, Lancet and NEJM	UK	May 2001	No specific speciality	33 RCTs included. 0 (0%) updated a SR. 3 (9%) cited SR	Little evidence exists to suggest the results of an RCT are discussed in light of the totality of the available evidence.
Clarke M, Chalmers I. (1998) [18]	To assess whether RCTs in 5 general medical journals discuss new results in light of available evidence.	Cross-sectional	RCTs published in Annals of Int Med, BMJ, JAMA, Lancet and NEJM	UK	May 1997	No specific speciality	26 RCTs included. 0 (0%) updated a SR. 6 (23%) cited SR	Little evidence exists to suggest journals have adequately implemented the CONSORT recommendation that results of an RCT be discussed in light of the totality of the available evidence.
Clarke M, Hopewell S. (2013) [30]	To assess whether RCTs in 5 general medical journals discuss new results in light of available evidence.	Cross-sectional	RCTs published in Annals of Int Med, BMJ, JAMA, Lancet and NEJM	UK	May 2012	No specific speciality	35 RCTs included. 2 (6%) updated an SR. 11 (31%) cited SR	Many trials still do not use SRs in their reporting.
Clarke M, Hopewell S, Chalmers I. (2007) [28]	To assess whether RCTs in 5 general medical journals discuss new results in light of available evidence.	Cross-sectional	RCTs published in Annals of Int Med, BMJ, JAMA, Lancet and NEJM	UK	May 2005	No specific speciality	18 RCTs included. 0 (0%) updated a SR. 5 (28%) cited SR	Little evidence suggests results of an RCT are discussed in light of the totality of the available evidence. Although the proportion of trials referring to SRs in ‘Discussion’ sections has increased, the majority of reports continued to fail even to do this.
Clarke M, Hopewell S, Chalmers I. (2010) [29]	To assess whether RCTs in 5 general medical journals discuss new results in light of available evidence.	Cross-sectional	RCTs published in Annals of Int Med, BMJ, JAMA, Lancet and NEJM	UK	May 2009	No specific speciality	29 RCTs included. 1 (4%) updated an SR. 10 (35%) cited SR	Little evidence exists to suggest results of an RCT are discussed in light of the totality of the available evidence. Although the proportion of trials referring to SRs has increased, most reports still fail to do this.
Engelking A, Cavar M, Puljak L. (2018) [26]	To analyse whether existing SRs were mentioned in RCTs published as a rationale for discussing the results.	Cross-sectional and meta-analysis	RCTs published in Anaesthesia, Anaesthesia and Analgesia, Anaesthesiology, Pain, British Journal of Anaesthesia, European Journal of Anaesthesiology, Regional Anaesthesia and Pain Medicine	Croatia	2014–2016	Anaesthesia, anaesthesia and analgesia, anaesthesiology, pain,	622 RCTs included. 245 (39%) cited SR	No conclusion regarding placing new results in contexts of earlier results in the discussion section
Goudie AC et al. (2010) [31]	To assess the extent to which authors currently make use of previous trial evidence in the reporting of RCTs.	Cross-sectional	RCTs published in JAMA and Archives of Internal Medicine	UK	January–May 2007	No specific speciality	27 RCTs included. 1 (4%) updated an SR. 10 (37%) cited SR	No conclusion regarding placing new results in contexts of earlier results in the discussion section
Helfer B et al. (2015) [32]	To assess whether recent meta-analyses cite, describe, and discuss previous meta-analyses and SRs.	Cross-sectional	Meta-analyses published in NEJM, Lancet, JAMA, Annals of Int Med, PLOS Medicine, BMJ (pharmacological treatment)	Germany	January 2012–March 2013	Pharmacological treatment	52 meta-analyses included. 25 (48%) cite SR	Meta-analyses on pharmacological treatments do not consistently discuss the findings of previous meta-analyses on the same topic.
Hoderlein X, Moseley AM, Elkins MR. (2017) [20]	To investigate the extent to which RCTs use high-quality clinical research to interpret the trial’s results and to assess a possible progress between 2001 and 2015.	Cross-sectional	Clinical trials randomly selected from Physiotherapy Evidence Database	Germany	2001 and 2015	Physiotherapy	2001: 70 RCTs included. 0 (0%) updated a SR. 12 (17%) cited SR. 2015: 151 RCTs included. 1 (1%) updated an SR. 52 (34%) cited SR	Citing is increasing from 2001 to 2015, but integration with existing research in the ‘Discussion’ section is rare.
Johnson AL, Walters C, Gray, H et al. (2020) [21]	To evaluate the use of SRs to justify RCTs…. And analyse the reference of SRs for trial justification in RCTs.	Cross-sectional	RCTs published in 3 high-ranking orthopaedic journals, and for comparison RCTs published in general orthopaedic journals	USA	January 1, 2015, to November 30, 2018	Orthopaedia	128 RCTs included. No data on SRs in the ‘Discussion’ section	SRs are frequently cited in orthopaedic trauma RCTs but are not commonly cited as justification for conducting a clinical trial.
Rauh S, Nigro T, Sims M et al. (2020) [22]	To analyse published articles for citation of SRs for justification of conducting RCTs.	Cross-sectional	RCTs in obstetrics and gynaecology journals	USA	January 1, 2014–December 31, 2017	Obstetrics and gynaecology	458 trials were included. 207 (45.2%) cited SRs	A large portion of the RCTs recently published in clinical obstetrics and gynaecology journals are not citing SRs as justification for conducting their studies, which may be leading to an increase in research waste.
Rosenthal R, Bucher HC, Dwan K. (2017) [23]	The aim was to investigate to what extent information from SRs is used to synthesise results.	Cross-sectional	RCTs published in Annals of Surgery, JAMA Surgery, British Journal of Surgery	Switzerland	2010	Surgery	51 RCTs included. 0 (0%) updated an SR. 9 (18%) cited SR	SRs are considered for summarising findings […] rather than for knowledge synthesis after trial conduct.
Shephard S, Wise A, Johnson BS et al. (2021) [19]	To appraise the use of SRs as justification in RCTs …and report the manner in which SRs were incorporated into RCT manuscripts published in those journals.	Cross-sectional	RCTs published in the top four urology journals based on Google Scholar h5 index	USA	November 30, 2014–November 30, 2019	Urology	276 RCTs included. No data on SRs in the ‘Discussion’ section	RCTs published in four high-impact urology journals inconsistently referenced an SR as justification, and 39.1% of our entire sample did not reference an SR at all.
Torgeson T, Evans S, Johnson BS et al. (2020) [25]	To evaluate the use of SRs to justify conducting RCTs in top ophthalmology and optometry journals.	Cross-sectional	RCTs published in the top five Google Scholar h-5 index journals Ophthalmology and Optometry	USA	December 5, 2018	Ophthalmology and optometry	152 RCTs included. 35 (23%) cited SR	Less than one quarter of phase III RCTs cited SRs as justification for conducting the RCT.
Walters C, Torgeson T, Fladie I et al. (2020) [24]	To evaluate whether RCTs … referenced SRs as the basis for conducting a trial.	Cross-sectional	RCTs published in three high-impact factor general medicine journals (NEJM, Lancet, JAMA)	USA	January 1, 2016–August 31, 2018	General medicine	637 RCTs included. No data on SRs in the “Discussion” section	Less than half of the analysed clinical trials cited SRs as the basis for undertaking the trial.