Equations are great – they provide a formal a description of the problem in hand, and often also handy, standardized way to arrive to a quantity of interest. In theory. A recent paper looking into published estimates of coefficient of additive genetic variation (CVA) - a standardized quantity invented to measure the amount of additive genetic variance, or rather evolvability, of a trait - finds that roughly 50% of the papers using this equation have made mistakes in calculations. Not only that the mistakes would of one particular kind, but that the same deceptively simple equation can be abused in bewilderingly different ways. Read and learn.
Garcia-Gonzalez et al. (2012) Comparing evolvabilities: common errors surrounding the calculation and use of coefficients of additive genetic variation. Evolution in press