Experimental Factor Ontology identifier EFO_0006988 (endophenotype) is measurable biological (physiological, biochemical, and anatomical features), behavioral (psychometric pattern) or cognitive markers that are found more often in individuals with a disease than in the general population. Because many endophenotypes are present before the disease onset and in individuals with heritable risk for disease such as unaffected family members, they can be used to help diagnose and search for causative genes.