Why does brain-to-body mass ratio inaccurately portray cognitive ability compared to encephalization quotient (EQ)? Because there is a distinction between brain parts that are necessary for the maintenance of the body and those that are associated with improved cognitive functions. There brain parts contributed to the overall weight of the brain.
brain-to-body mass ratio, also known as the brain-to-body weight ratio, is the ratio of brain mass to body mass, which is hypothesized to be a rough estimate of the intelligence of an animal, although fairly inaccurate in many cases. A more complex measurement, encephalization quotient (EQ), takes into account allometric effects of widely divergent body sizes across several taxa. The raw brain-to-body mass ratio is however simpler to come by, and is still a useful tool for comparing encephalization within species or between fairly closely related species. *