The performance of an arithmetic operation upon a variable (e.g., taking the natural log of a variable or subtracting a constant). Data for an <a href="search.pl?p=econometric model">econometric model</a> are often transformed by taking the logs of all variables, creating a so-called <a href="search.pl?p=log-log model">log-log model</a>. <o:p></o:p></P>