Yesterday wrote a post for Search Engine Land titled Free Tool For Back-Of-The-Napkin Paid Search Forecasting. A summary:
Sometimes marketers need quick back-of-the-napkin projections of search advertising elasticity.
The common question goes something like “So if we got really aggressive and doubled our Google spend next month, about how much would our sales go up?”
True elasticity optimization comes through testing, and true forecasting takes patience and care.
But when you need fast back-of-the-napkin guestimates of sales for a given ad spend, the "Square Root Rule" can be a useful tool.
The “Square Root Rule” a simple mathematical statement which assumes the relationship between sales and advertising follows a square root relationship.
This assumption is utterly wrong, but, even so, the rule can often be useful...