Demand Elasticity

Imagine tracking snacks sold by one stall during a day. We care about the size of the response, not merely that somebody leaves after a price rise. With ordinary downward-sloping demand, the ratio of percentage changes is negative: price rises while quantity falls. It is therefore often reported as a magnitude without the minus sign. Elasticity has no unit, whereas a line’s slope depends on the graph’s units. Merely changing the units used to write down the same prices does not change customers’ behaviour; what matters is specifying whose purchases and which period we observe. Marginal Utility adds the perspective of how useful another item is to that person; elasticity measures the quantity response to price. [1] [6]

For simplicity, use illustrative prices of 10 and 12 and daily quantities of 100 and 80. The midpoint method divides each change by the average of its old and new values: (-20 / 90) / (2 / 11) = -11/9, approximately -1.22. The magnitude is 1.22. Using the original values as bases instead gives -1, a magnitude of 1. Do not mix these methods. The midpoint method preserves the magnitude when the comparison is reversed. These figures explain the calculation; they are not measurements of a real stall or the Bitcoin market. [1]

Using the coefficient’s magnitude without its sign, a value above 1 means quantity responds proportionally more than price, below 1 less, and exactly 1 equally. These cases are called elastic, inelastic and unit-elastic demand. Inelastic does not mean no response; that requires 0. Nor does one calculated interval describe every possible price. Customers might accept a small price rise but change their minds at a substantially higher price. [1]

A customer might bring a snack from home tomorrow. Changing household or business equipment, however, often takes time and money: working equipment is not normally replaced immediately. Available alternatives and whether we examine the short or long run therefore matter. Demand for snacks from one particular stall is also different from demand for food generally. A longer horizon does not itself guarantee a particular coefficient; it may simply open options unavailable today. [2]

In our example, revenue changes from 1000 to 960: fewer items sell even though each costs more. Revenue is price multiplied by quantity sold. Along unchanged downward-sloping demand over an elastic interval, a price increase therefore reduces revenue. Revenue is not profit, though. Profit also requires accounting for materials, labour and operating costs. Elasticity alone cannot tell the owner which price will produce the best business result. [2]

The price rise might coincide with a holiday that empties nearby offices. The sales decline cannot then all be attributed to the new price. Economics distinguishes movement along a demand curve, where the good’s own price changes while other conditions stay fixed, from a shift of the whole curve when income, preferences or expectations change. Observed prices and quantities alone do not isolate price elasticity. A useful estimate explains how it separated these simultaneous influences. [4]

Customers might also buy more after their income rises. Again, we compare percentage changes: income elasticity relates the change in quantity bought to the change in income, while cross-price elasticity relates it to the change in another product’s price. If an alternative, such as a similar snack elsewhere, becomes more expensive, demand for our product may rise: a positive cross-price coefficient generally indicates substitutes. For goods bought together it is usually negative, since one becoming more expensive can reduce purchases of the other. Each calculation therefore compares a different pair of changes and answers a different question; these results alone do not establish sensitivity to the product’s own price. [3]

Bitcoin.org links market price to supply and demand and describes predictable issuance. The 21 Million rule is not a measure of buyers’ response, however. When examining demand for bitcoin (BTC), distinguish the number of coins purchased, spending in ordinary currency and trading volume. The same cash budget buys fewer coins at a higher price; high turnover alone does not reveal the full relationship between price and willingness to buy. Neither the issuance limit nor turnover proves a particular coefficient or future price growth. Supply Elasticity examines the other side of the market: sellers’ response. [5]