Bottom-up approach. No matter what you do (waiting in a line in the shop, optimizing your pick-up strategy in a pub, or estimating the market for senior care in Ivy) you will most likely use this method to get a rough estimation of a specific phenomenon. The technique is very simple: you find a typical user, estimate his consumption of a specific good and then by estimating how many users you have you can get to a rough estimation of the market size. Below is a short movie showing how it works in practice: