Obsolescence of the literature: A study of included studies in Cochrane reviews

Ageing or obsolescence describes the process of declining use of a particular publication over time and can affect the results of a citation analyses as the length of citation window can change rankings. Obsolescence may not only vary across fields but also across subfields or sub-disciplines. The aim of this study is to determine the sub-disciplinary differences of obsolescence on a larger scale allowing for differences over time as well. The study presents the results of an analysis of 82,759 references across 53 healthcare and health policy topics. The references in this study are extracted from systematic reviews published from 2012 to 2016. The analyses of obsolescence include median citation age and mean citation age. This study finds that the median citation age and the mean citation age differ considerably across groups. For the latter indicator, an analysis of the confidence intervals confirms these differences. Using the subfield categorisation from Cochrane review groups, we found larger differences across subfields than in the citing half-lives published by Journal Citation Reports. Obsolescence is important to consider when setting the length of the citation windows. This study emphasises the vast differences across health sciences subfields. The length of the citation period is thus highly important for the results of a bibliometric evaluation or study covering fields with very varying obsolescence rates.

Does the citation period have any effect on the informative value of selected citation indicators in research evaluations?

To date, there has not been any definitive statement for bibliometric analyses from the scientific community as to how long to make the period for analysis in order to guarantee the maximum possible validity of citation analyses. Up to now, it has been particularly unclear as to whether different disciplines and citation indicators have any effect on what period for analysis to select. This is why this study aims to provide answers to these issues. Therefore, publications in the fields of business studies, biology, and medicine from 2007 to 2009 are surveyed. The citations from ten separate consecutive citation periods from 2009 up to 2018 are generated for these publications from Web of Science and selected citation indicators are calculated for them. The results show that the fundamental validity of citation indicators increases with time. However, if the goal of the analyses is to establish a ranking order, then even short citation periods are informative. Our results are stable in terms of the disciplines, although differences do occur in the citation indicators under consideration.

Impact of automated photo enforcement of vehicle speed in school zones: interrupted time series analysis

ObjectiveMeasure the impact of automated photo speed enforcement in school zones on motorist speed and speeding violation rates during school travel.MethodsAutomated enforcement cameras, active during school commuting hours, were installed around four elementary schools in Seattle, Washington, USA in 2012. We examined the effect of automated enforcement on motorist speeds and speed violation rates during the citation period (10 December 2012 to 15 January 2015) compared with the ‘warning’ period (1 November to 9 December 2012). We evaluated outcomes with an interrupted time series approach using multilevel mixed linear regression.ResultsMotorist speed violation rates decreased by nearly half in the citation period compared with the warning period (standardised incident rate ratio 0.53, 95% CI 0.42 to 0.66). The hourly maximum violation speed and mean hourly speeds decreased 2.1 MPH (95% CI –2.88 to –1.39) and 1.1 MPH (95% CI –1.64 to – 0.60), respectively. The impact of automated enforcement was sustained during the second year of implementation.ConclusionAutomated photo enforcement of speed limit in school zones was effective at reducing motorist speed violations and also achieved a significant reduction in mean motorist speed.