Rebecca Turner (MRC Biostatistics Unit)

Bias adjustment in evidence synthesis

Policy decisions often require synthesis of evidence from multiple sources, and the source studies typically vary in rigour and in relevance to the target question. Rigour (or internal bias) reflects how well a study estimates its intended parameters. In a study comparing the effectiveness of two interventions, rigour varies according to use of randomisation, degree of blinding and attrition levels. Relevance (or external bias) reflects how similar the source study design is to the target setting, with respect to study population, outcomes and interventions. In this talk, methods for allowing for internal and external biases in evidence synthesis are presented, and illustrated through application to examples in antenatal care and obesity. A generic bias modelling approach allows decisions to be based on all available evidence, with less rigorous or less relevant evidence discounted using computationally simple methods.