Which one of the following will be affected by inter- observer variation in epidemiological studies

the term sensitivity was introduced by Yerushalmy in 1940 s as a statistical index of diagnostic accuracy.it has been defined as the ability of a test to identify correctly all those who have the disease that is true positive.it also gets affected by the intern observer variations in the epidemiological studies. ref:park&;s textbook of preventive and social medicine,22 nd edition,pg no 131 .