Own Price, Cross Price and Income Elasticity

We studied elasticity in a previous post:

The percentage change in quantity demanded, given a percentage change in price.

In today’s post, we expand the definition of elasticity a little. That naturally makes it a little complicated, but it also enriches our understanding of it – a good bargain.

What if the price of a substitute changes? What if, that is, the price of Coke changes a little. By what percentage will the quantity demanded of Pepsi change? The measurement of such a thing is called cross price elasticity (substitute).

The percentage change in quantity demanded, given a percentage change in the price of a substitute.

The first definition above is therefore the definition of own price elasticity, while the second one is of cross price elasticity. Cross price elasticity, naturally, will be of twp types – that of complements, and that of substitutes.

There is yet a fourth type of elasticity, called income elasticity of demand. As you might imagine, it is

The percentage change in quantity demanded, given a percentage change in income.

Say your income in a particular month goes down by 10 percent. Is it reasonable to imagine that you will therefore cut back on your consumption of movies in a theatre, or dinners in restaurants? Unless you are a hardcore movie buff, or love eating out a lot, the answer would probably be yes. The income elasticity of demand for these goods is therefore high.

On the other hand, will you cut back your consumption of pills prescribed by your doctor? Almost definitely not, right? The income elasticity of demand for these goods is therefore low.

And that concludes our series on the basics of supply and demand!

Here’s a quick recap:

The demand (and supply) of a good depends upon:

  1.  it’s own price
  2. the price of complements and substitutes
  3. it’s own price elasticity
  4. the cross price elasticities
  5. the income elasticity
  6. changing tastes and preferences
  7. changing incomes

As you can no doubt see, thinking about demand is fairly complex – but it is, nonetheless, rewarding. In the next post, we’ll give you a list of resources for learning more about demand and supply (as we did for the Solow model), and then begin a new topic.


Tastes, Preferences and Income

Remember CD’s? They used to be the last word in convenient storage, and if you are of a particular age or higher “AVSEQ01.dat” will be a very evocative term indeed.

CD’s these days are available for around 15 rupees each, down from about 50 rupees a while ago, and maybe even higher. The law of demand that we have been learning about all this while suggests that the demand for CD’s should go up, since the price has come down.

Ah, but who uses CD’s these days? All the music you’d ever want to listen to and more is available on multiple streaming services. YouTube ensures that you have more video content to watch than is humanly possible, while services such as Netflix and Amazon Prime have made CD and DVD players ancient relics.

In other words, tastes and preferences of people have changed, and they will not want to buy CD’s, no matter the cost. So it’s not just the price of a good, nor that of complements and substitutes that matters – it also is whether or not you want to buy the good at all or not.

And to complicate matters even further, it’s not just tastes and preferences – it’s also income!

Remember dalda? Every Indian household used to use it in the 1980’s, but families today won’t go within sniffing distance of the stuff. That’s because, generally speaking, incomes have been rising, and households now have the money to make health-conscious choices – which means dalda is out, not matter the price.

And you could say the same thing for landlines, cassette recorders, cathode ray televisions, desktops, dumbphones – and that’s just from the world of electronics. As societies progress, they experience a rise in incomes and a change in tastes and preferences – and these things impact both the demand and supply of goods.

So, in a nutshell:

The price of a good, its elasticity, the price of its complements and substitutes, changes in incomes, tastes and preferences all impact the demand (and supply) of a particular good.

Next, we’ll take a look at cross price elasticity and income elasticity.

Complements and Substitutes

Two simple concepts, but really important ones.

When we speak about the demand of, and the supply of any particular thing, it is impacted by a variety of factors. One of these factors is the existence of substitutes and complements.

What are substitutes, and what are complements?

Say you walk into a store at the height of summer, thirsting for a nice, ice-cold cola. If you ask for a can of Coke, and upon being told that Coke isn’t available but Pepsi is, drink that can of Pepsi – well, then, you have “substituted” Pepsi for Coke. Goods that can act as a replacement for each other are substitutes.

These substitutes can be near/far substitutes. If no cola drink is available, and you drink nimbu sharbat instead, that is also a substitute. If you just have a glass of water instead of  a cola, well, that is also a substitute. Pepsi would be a close substitute, while water, arguably would be a not so close substitute.

Complements, on the other hand, are things that go well with, or must be used with, the good in question. Who ever heard of a flat screen TV without a set-top box? Of what use is a plate of pakoras in the monsoons without a hot cup of adrak wali chai? These become complements.

Now the reason these concepts are important is because they help us predict demand better. Say Coke sells its cans for 30 rupees, but Pepsi lowers prices to 20. Will the demand for Coke go up or down? Down, naturally, because a close substitute is available at a lower price.

When the price of a close substitute goes up, the demand for the good in question rises, and vice versa.

Generally speaking the closer the substitute, the more worried you should be about the price. Maruti Suzuki won’t lose sleep over its pricing of the Alto if Rolls Royce ups the prices on its models. Strictly speaking, these are substitutes – but not really. On the other hand, if Hyundai lowers the price on Eon (a very close substitute to the Alto), Maruti Suzuki will pay very, very close attention.

Also, the higher the number of susbtitutes, the lesser your ability to raise prices. Who ever heard of a chaiwalla selling tea at 20? It simply doesn’t make sense, because you can typically walk less than 100 meters to find a another chaiwalla selling an equally good cup of tea for the going rate.

And what about complements? Well, it’s easy to think through this. If the price of set-top boxes rises, the demand for flat-screen TV’s will go down. Think about it – you have to factor in not just the cost of the TV, but also the thing that makes the TV useful in the first place. So as a whole package, if the cost is going to go up, well, demand will go down.

When the price of a complement goes up, the demand for the good in question falls, and vice versa.

Complements and substitutes affect the demand for goods, and are also important concepts in the field of marketing.

Next up, we’ll take a look at changing tastes and preferences.

3 factors that impact demand and supply

The Gurugram story that we learnt about in the previous post was a fairly simple one. We spoke about how people on both sides of the divide (demand and supply) think about prices and therefore their decisions about how much to supply and how much to demand. Alas, if it were only that simple.

As it turns out, there are many, many other factors at play when it comes to thinking about demand and supply. In this post, we are going to list out these factors, and in the posts to follow, we’re going to speak about each one of them in turn.

First, the existence of things that may be substitutes, and things that may be complements to the thing being analyzed. For example, flats/apartments may be one thing, but what about bungalows? A bungalow is a substitute for an apartment. Will a change in the price of bungalows affect the demand for apartments? If so, how? Buying an apartment also means, presumably, hiring an interior decorator.  Will the rates being charged by an interior decorator impact the decision to buy a flat? This is the analysis of complementary goods and substitute goods – one part of the puzzle.

Second, a change in taste and preferences. For example, with a rise in incomes, people may not want to stay in apartments, but in bungalows. Conversely, if there is a fall in income, people may not want to stay in apartments, but in slums. These things also impact our analysis.

Third, how sensitive is demand to a change in price. Very large changes in prices may not impact the demand for cigarettes all that much (and any finance minister worth his salt will tell you this), while very small changes in price will change the demand for jewellery significantly.

Each of these are factors that impact significantly both the demand and supply of a good, as as we mentioned, in the three posts that follow, we will take a look at each one of them, beginning with the third factor listed above: elasticity.