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Table 1 Factors affecting a decision of whether to conduct an update or amendment to an existing systematic review or map

From: Updating and amending systematic reviews and systematic maps in environmental management

Where it may be valuable to conduct an update Where it may be valuable to conduct an amendment Where it may not be valuable to consider an update or amendment
Where a topic is still relevant to policy and practice, and scoping suggests that there are new studies suitable for inclusion
Where a topic or intervention is relatively new and so limited data existed for the original synthesis, and it is recognised that an update would provide valuable additional information
Where large volumes of information have been published over a short timescale, for example for topical issues (e.g. pollinators) or broad areas (e.g. climate change), especially where evidence is contentious or where trends in research methods, study subjects, research groups or dogma have demonstrated a shift over time—new evidence may be more likely to contradict old
Where large influential studies have been published that may affect the outcomes of the original synthesis
Where new secondary synthesis methods allow a more precise or accurate investigation or the available data
Where the evidence base now contains enough studies to examine a source of heterogeneity previously not investigable
Where the review may benefit from the inclusion of additional sources of information, for example where evidence may be released under embargo (GMO, sensitive research)
Where previous research has been retracted or previous primary research methods proved to be inappropriate;
Where methods used in the original review or map are contentious, outdated or missing
Where new primary research methods mean a more accurate or more precise data set for synthesis but will require new approaches to synthesis (such as the inclusion of new sub-groups for analysis)
Where no more research has been conducted on a topic (e.g. because policy or practice has changed) Where insufficient time has elapsed for more data to have been produced
Where there are studies underway that could usefully be included in the future and it would be better to wait until they become available
Where there is now limited policy or practical interest in the topic, so resources could be better allocated elsewhere