Argues that the law of demand is the most famous in economics and is also the truest law for many economists. One reason for this belief is that elasticities allow economists to quantify differences between markets without standardizing units of measurement (Aycock, 2010). The law of demand explains that, all other things being equal, when the price of a good increases, the quantity demanded will decrease, and when the price of a good decreases, the quantity demanded will increase. In terms of elasticity, price elasticity of demand (PED) measures consumers' sensitivity to a change in price (McConnell et al., 2015, p.134). Prices are elastic when a change in price causes a greater percentage change in quantity demanded. For example, if the price of a Snickers bar drops 20% but demand increases 80%, PED = -4.0. This price change could push consumers to purchase alternative chocolate bars. Inelastic price changes cause a smaller percentage change in quantity demanded. If the price of tobacco falls by 30% but demand increases by only 10%, PED = -0.33. Since it is addictive and has no substitute, if the price of cigarettes increases, people who smoke will likely continue to do so (Pettinger,