Allometry is used to describe the morphological evolution of species, and is based on the relation between an organism's size and the size of any part of the organism.
Allometry is studied during the growth of a single organism; as a comparison between different organisms of the same species; and between organisms in different species. The allometric equation is graphed on an XY axis, with the body size on the x-axis and the part size on the y-axis. The scatter produced by the different measurements being compared can then be analyzed for useful data.
Allometry allows scientists to study biological functions as they increase as a power of body size. For instance, more energy is consumed by an elephant, but a mouse probably consumes more energy when that energy is measured as a function of mouse body weight.
The allometric equation is generally stated as
y = mx + b
where y = predicted size of body part; x = observed body weight; m = slope acquired; and b = the value of y where it intercepts the vertical axis.
Not all allometric comparisons are linear; the allometric equation is frequently modified to compensate for this. The point is to determine a consistent relationship for the species in question.
Another allometric equation that compensates for nonlinear functions is:
log(y) = log(b) + m[log(x)]
Web Resources On Allometry Equation
Application of allometric analyses to some primate problems
Sauropods, Elephants, Weightlifters
Book Resources On Allometry Equation
The Allometry of Growth and Reproduction by M. J. Reiss
Plant Allometry : The Scaling of Form and Process by Karl J. Niklas