Using the association between feed characteristics and Salmonella prevalence we will present an approach to combining data with multiple outcomes from multiple studies designs. The approach may be a method of informing policy makers in the area of food safety when a large amount of heterogeneous literature is available about a topic. The procedure for a systematic review of the literature was followed until the synthesis component. However, to combine the evidence we modified of the FDA Interim Evidence Ranking System for Scientific Information. Each study was characterized as one of 5 study design types based on evidentiary value. After classification by evidentiary value, the studies were considered collectively to rate the strength of the body of evidence based on quantity and consistency. The quantity ranking considered the number of studies, the number of individuals studied and generalizability to the target population. The consistency ranking considered whether studies with different designs reported similar findings. After ranking the body of evidence, an overall ranking was assigned for the strength of the evidence. The final ranking system had four levels. For example, the highest rank of scientific evidence, reflects a high level of comfort among qualified scientists that the association/relationship is scientifically valid. This level ranked relationship would be considered to have a very low probability of significant new data overturning the conclusion that the relationship is valid or significantly changing the nature of the relationship.
Available at: http://works.bepress.com/annette_oconnor/8/