Why are indices better than simple measurements for comparing fossil specimens?

Indices are used to study fossil specimens and compare them against each other. They are based on concept of ratio hence better than simple measurements when it comes to comparative analysis. They compensate for the problems caused by other variable factors like size or specimen.

For example, to estimate if an organism is long or round headed simple measurement of cranial length or breadth can be done and the result can be given according to the selected parameter. However some specimens will have longer breadth than length and some will have longer length than breadth. So, it is better to measure both the parameters and find out their ratio. Hence, cranial index is used which is given by: (Cranial breadth/Cranial length) * 100.