Type of bias

Description

Relevant domains in the Collaboration’s ‘Risk of bias’ tool

Selection bias.

Systematic differences between baseline characteristics of the groups that are compared.

• Sequence generation;

• Allocation concealment.

Performance bias.

Systematic differences between groups in the care that is provided, or in exposure to factors other than the interventions of interest.

• Blinding of participants, personnel and outcome assessors;

• Other potential threats to validity.

Attrition bias.

Systematic differences between groups in withdrawals from a study.

• Incomplete outcome data;

• Blinding of participants, personnel and outcome assessors.

Detection bias.

Systematic differences between groups in how outcomes are determined.

• Blinding of participants, personnel and outcome assessors;

• Other potential threats to validity.

Reporting bias.

Systematic differences between reported and unreported findings.

• Selective outcome reporting;

• (see also Chapter 10).