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ObjectivesIn the process of scientific progress, prior evidence is both relied on and supplanted by new discoveries. We use the term ‘knowledge half-life’ to refer to the phenomenon in which older knowledge is discounted in favour of newer research. By quantifying the knowledge half-life, we sought to determine whether research published in more recent years is preferentially cited over older research in medical and scientific articles.DesignAn observational study employing a directed, systematic search of current literature.Data sourcesBMJ,PNAS,JAMA,NEJM,The Annals of Internal Medicine,The Lancet,ScienceandNaturewere searched.Eligibility criteria for selecting studiesEight high-impact medical and scientific journals were sampled examining original research articles from the first issue of every year over a 25-year span (1996–2020). The outcome of interest was the difference between the publication year of the article and references cited, termed ‘citation lag’.Data extraction and synthesisAnalysis of variance was used to identify significant differences in citation lag.ResultsA total of 726 articles and 17 895 references were included with a mean citation lag of 7.5±8.4 years. Across all journals, >70% of references had been published within 10 years of the citing article. Approximately 15%–20% of referenced articles were 10–19 years old, and articles more than 20 years old were cited infrequently. Medical journals articles had references with significantly shorter citation lags compared with general science journals (p≤0.01). Articles published before 2009 had references with significantly shorter citation lags compared with those published in 2010–2020 (pConclusionsThis study found evidence of a small increase in the citation of older research in medical and scientific literature over the past decade. This phenomenon deserves further characterisation and scrutiny to ensure that ‘old knowledge’ is not being lost.

IntroductionEsketamine is the S-enantiomer of racemic ketamine and has been approved by the Food and Drug Administration for the management of treatment resistant depression, demonstrating effective and long-lasting benefits. The objective of this observational study is to elucidate the association of intranasal (IN) esketamine with beneficial and negative outcomes in the management of treatment resistant major depressive disorder.Methods and analysisThis is a multicentre prospective cohort observational study of naturalistic clinical practice. We expect to recruit 10 patients per research centre (6 centres, total 60 subjects). After approval to receive IN esketamine as part of their standard of care management of moderate to severe treatment resistant depression, patients will be invited to participate in this study. Association of esketamine treatment with outcomes in the management of depression will be assessed by measuring the severity of depression symptoms using the Montgomery-Åsberg Depression Rating Scale (MADRS), and tolerability by systematically tracking common side effects of ketamine treatment, dissociation using the simplified 6-Item Clinician Administered Dissociative Symptom Scale and potential for abuse using the Likeability and Craving Questionnaire (LCQ). Change in depressive symptoms (MADRS total scores) over time will be evaluated by within-subject repeated measures analysis of variance. We will calculate the relative risk associated with the beneficial (reduction in total scores for depression) outcomes, and the side effect and dropout rates (tolerability) of adding IN esketamine to patients’ current pharmacological treatments. Covariate analysis will assess the impact of site and demographic variables on treatment outcomes.Ethics and disseminationApproval to perform this study was obtained through the Health Sciences Research Ethics Board at Queen’s University. Findings will be shared among collaborators, through departmental meetings, presented on different academic venues and publishing our manuscript.

Objective This research aims to determine the long-term impact of the Bloor Street Viaduct suicide barrier on rates of suicide in Toronto and whether media reporting had any impact on suicide rates. Design Natural experiment. Setting City of Toronto, Canada; records at the chief coroner’s office of Ontario 1993–2003 (11 years before the barrier) and 2004–2014 (11 years after the barrier). Participants 5403 people who died by suicide in the city of Toronto. Main outcome measure Changes in yearly rates of suicide by jumping at Bloor Street Viaduct, other bridges including nearest comparison bridge and walking distance bridges, and buildings, and by other means. Results Suicide rates at the Bloor Street Viaduct declined from 9.0 deaths/year before the barrier to 0.1 deaths/year after the barrier (incidence rate ratio (IRR) 0.005, 95% CI 0.0005 to 0.19, p=0.002). Suicide deaths from bridges in Toronto also declined significantly (IRR 0.53, 95% CI 0.40 to 0.71, p