Final answer:
The most widely used method for bilirubin measurement is the Jendrassik Grof method.
Step-by-step explanation:
The most widely used method for bilirubin measurement is the Jendrassik Grof method. This method is based on the reduction of bilirubin and the subsequent reaction with a coloring agent to produce a color change that is proportional to the amount of bilirubin present. Other methods such as the Jaffe reaction, Schales and Schales method, and 8-hydroxyquinoline reaction are also used for bilirubin measurement, but they are not as widely used as the Jendrassik Grof method.