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Table 2 Criteria for study validity assessment

From: Management of UK priority invasive alien plants: a systematic review protocol

Question/criterionResponse to questionType of bias addressed
YesPartiallyNoUnclear
Did the study consist of both temporal and spatial comparisons?Before-after-control-impact studyBefore-and-after study or controlled studyN/A as study is not eligible for inclusion based on inclusion criteriaLacking sufficient information to judgeSelection bias
Did the study use randomization?Study accounts for spatial heterogeneity by using appropriate randomisation of samplesN/A as study was either randomized with respect to the management intervention or not (e.g. random site selection but not random allocation of treatments/controls)Study does not attempt to randomize samplingLacking sufficient information to judgeSelection bias
Did the study avoid confounding factors?Confounding factors were likely to be minimal as a result of blocking/pairing or stated attempts to match samplesSome confounding factors present, likely to have a moderate impact on outcomeStudy was subject to confounding factors that could have a major impact on the outcomeLacking sufficient information to judgeSelection bias and performance bias
Can the study determine causality?Experimental study in which comparator samples were selected prior to the management intervention being usedCorrelative study in which comparators are selected after the management intervention has already been implemented, thereby limiting the ability of researchers to determine the similarity of comparators prior to management intervention useN/A—studies with no comparator will be excludedLacking sufficient information to judgeSelection bias and performance bias