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Table 1 Direction of bias on study outcome for each key question

From: Methodological limitations in experimental studies on symptom development in individuals with idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF) – a systematic review

Bias direction Within domain/key question Methodological alternatives considered a source of high risk of bias
In favour of an effect of exposure (+) Performance bias:
- Was the level and method of blinding appropriate?
- no blinding of research personal during sessions
- insufficient removal of any clues that could reveal exposure status and no tests done to control blinding
In favour of a null result (−) Selection bias:
- Were individuals excluded whose symptoms may be explained by somatic diseases or mental disorders? - not sufficiently considered/not reported
- Was the contrast in the severity of symptoms between situations with/without exposure verified? - not reported
- Were EMF exposures (type of exposure source, frequency range and exposure level) applied that individuals associate with their symptoms? - not reported
- Were exposure durations and assessment times applied that matched the time scales for the symptoms to appear? - not reported
- Were the symptoms registered in the trials matched with those experienced in everyday exposure situations? - not reported
Exposure bias:
- Was the background exposure level controlled and minimized? - not reported
- Was the exposure level controlled? - not reported
Uncertain direction on study outcome (±) Selection bias:
- Were the intervals between exposure sessions sufficiently long to allow for recovery and to avoid carry-over effects? - not reported
Performance bias:
- Were biases related to sequence and period of the exposure conditions minimized (for studies with cross-over design)? - same sequence and period of the exposure conditions for all participants or for all participants of a group
- not reported
Confounding bias:
- Were biases related to confounders and cofactors minimized (for studies comparing parallel groups of IEI-EMF participants with different exposure conditions)? - not randomized
Attrition bias:  
- Were biases minimized that are related to attrition and to incomplete data included in the analysis? - high attrition/exclusion rate or incomplete data in analysis
Selective reporting bias:  
- Was bias related to selective outcome reporting minimized? - selective outcome reporting