Systematic Bias

Systematic bias refers to any consistent error in study design, conduct, or analysis that produces results that systematically deviate from the true effect. Common biases in supplement research include selection bias (non-random group assignment), performance bias (participants or providers behaving differently based on group knowledge), detection bias (outcome assessors knowing group assignments), attrition bias (differential dropout), and reporting bias (selective outcome reporting). Tools like the Cochrane Risk of Bias tool assess these domains. Industry-sponsored supplement studies are more likely to report positive results, suggesting potential sponsorship bias.