The mathematical measure of brain size relative to body size; the greater this value, the "more brain" a species has for their size. 

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Brain size varies among species and is mostly relative to the general size of the animal. It is not an automatic indicator of behavioral capability. 

Brain Size 

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Encephalization Factor  

There is a link between the increased size of specific brain structures and the necessity of the behavior/capability it is responsible for in some species (i.e., those that rely heavily on their sense of smell possess a relatively large olfactory bulb). Likely occur through the process of natural selection favoring individuals that adapted to improve that capability.

Brain Size & Behavior 

Researchers graphed these two characteristics to find a general mathematical relationship to study and examine the correlation between brain size and body weight. This graph shows the relationship between these two characteristics for mammals. 

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