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Table 3 Critical appraisal criteria

From: Biochar’s effect on the ecosystem services provided by sandy-textured and contaminated sandy soils: a systematic review protocol

Factor Low risk of bias Moderate risk of bias High risk of bias
Study design Experimental studies (treatment vs control) Quasi-experimental studies (including concurrent controls) Case studies and observational studies
Objectives/hypothesis Clear relation between objectives and methodology Clear relation between objectives and methodology No relation between objectives and methodology
Sampling Sampling method is suitable for gathering data on the population of interest The method used for sampling is appropriate for data gathering on population of interest Sampling method is not suitable for the population of interest
Replicates are proper (interventions are replicated) Replicates are proper
Intervention and comparator areas are well-matched (soil conditions are the same) Intervention and comparator areas are well-matched (soil conditions do not differ profoundly)
Confounding factors not present (both intervention and comparator sites are treated equally) Confounding factors not present (both intervention and comparator sites are treated equally)
Consideration of heterogeneity/effect modifiers Precisely determined/considered effect modifiers Effect modifiers are considered Effect modifiers not considered or determined
Statistical analysis Clear description of statistical analysis and results Statistical analysis and results are clear enough Not appropriate statistical analysis and results