//= getAssetHref('js/MainScripts/main.js') ?>
The variable that is substituted for an unobserved explanatory variable in a model. It is often used when it is infeasible or too expensive to use a more relevant variable. (For example, to use income as a measure of ability to purchase, even though it does not fully represent it, because the ability to purchase depends also on wealth, unreported income, gifts, etc.).