12 We assessed risk of bias in random sequence generation and allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias) and selective reporting (reporting bias).
Strobl, C., Boulesteix, A. L., Zeileis, A. & Hothorn, T. Bias in random forest variable importance measures: illustrations, sources and a solution.
Study design issues deserving attention include possible biases in random digit dialing control selection, consideration of the temporal course of exposure and disease, and acquisition of the necessary information to assess the potential value of ecologic studies.
Phenotypic bias in a random mutagenesis experiment is common, and studies cannot obtain random abnormal traits.
However, we will conduct a sensitivity analysis excluding studies with an unclear or high risk of bias in the random sequence generation or allocation concealment fields.
The large number of probes per target was expected to improve sensitivity, an important consideration given possible amplification bias in the random PCR sample preparation protocol, which could result in nonamplification of genome regions targeted by some probes [ 7].
To avoid bias in the random sampling of cDNA genes from Anthopleura elegantissima, similar proportions of library clones from the two conditions to be compared (aposymbiotic and symbiotic) were arrayed.
As would be expected, studies that demonstrated a potential risk of bias in ensuring random sequence generation, posed a similar risk of lack of allocation concealment [ 6, 9, 65, 73].
Poorly measured exposure data can produce differential errors leading to systematic bias or result in random errors or imprecision, which (unless corrected) typically lead to bias toward no effect (Bernardinelli et al. 1997).
Using the Cochrane Collaboration tool [22], two reviewers (CL and SS) independently assessed each study for risk of bias in seven domains: random sequence generation, allocation concealment, blinding of patients and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other sources of bias.
Therefore, a systematic analytical bias, in addition to random error, must be suspected.
