Table 1 Hierarchy of quality of evidence based on the information provided in the documents

From: Does production of oil palm, soybean, or jatropha change biodiversity and ecosystem functions in tropical forests

Category Quality of evidence presented
I Randomized controlled trials of adequate spatial and temporal scale for the study species
II Controlled trials without randomization with adequate spatial and temporal scale for the study species
III Comparisons of differences between sites with and without controls with adequate spatial and temporal scale for the study species.
IV Evidence obtained from multiple time series or from dramatic results in uncontrolled experiments.
V Opinions of respected authorities based on qualitative field evidence, descriptive studies or reports of expert committees.
VI Evidence inadequate owing to problems of methodology e.g. sample size, spatial or temporal scale.
  1. Modified after Pullin and Knight [15].