Figure 2.

Primary functions of biomarkers in all included studies. Categories of biomarker function were devised using an informal classification, designed to capture the breadth of biomarker function in included studies. Segments represent the number of biomarker studies examining biomarkers with a given primary function (n). Studies examining multiple biomarkers which have more than one function or single biomarkers with multiple functions may be represented in more than one segment of the ring chart. [Colour figure can be viewed at wileyonlinelibrary.com]