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Table 2 Guidance for assessing risk of selection bias at different study designs

From: What are the effects of control of mosquitoes and other nematoceran Diptera using the microbial agent Bacillus thuringiensis israelensis (Bti) on aquatic and terrestrial ecosystems? A systematic review protocol

Study design

Treatment and control areas

Randomisation of treatment allocation

Risk of selection bias

BA

Treatment and control in same area

N/A

Low

CI

Independent groups (spatially independent replicated controls and exposure areas)

Yes

Probably low/probably high

No

High/probably high

Unclear

Unclear

Matched pairs (one control and one exposure area in each replicate)

Yes, within pairs

Low

No

Probably high

Unclear

Unclear

BACI

Independent groups or matched pairs

Yes or No

Low/probably low