11 curves most frequently used in Economics

1. Production Possibility Curve

A production–possibility frontier (PPF) or production possibility curve (PPC) is a curve which shows various combinations of the amounts of two goods which can be produced with the given resources and technology, where the given resources are fully and efficiently utilized per unit time. A PPF illustrates several economic concepts, such as allocative efficiency, economies of scale, opportunity cost (or marginal rate of transformation), productive efficiency, and scarcity of resources (the fundamental economic problem that all societies face).

This tradeoff is usually considered for an economy, but also applies to each individual, household, and economic organization. One good can only be produced by diverting resources from other goods, and so by producing less of them.

Graphically bounding the production set for fixed input quantities, the PPF curve shows the maximum possible production level of one commodity for any given production level of the other, given the existing state of technology. By doing so, it defines productive efficiency in the context of that production set: a point on the frontier indicates efficient use of the available inputs (such as points B, D and C in the graph), a point beneath the curve (such as A) indicates inefficiency, and a point beyond the curve (such as X) indicates impossibility.

PPFs are normally drawn as bulging upwards or outwards from the origin (“concave” when viewed from the origin), but they can be represented as bulging downward (inwards) or linear (straight), depending on a number of assumptions.

An outward shift of the PPC results from growth of the availability of inputs, such as physical capital or labour, or from technological progressin knowledge of how to transform inputs into outputs. Such a shift reflects, for instance, economic growth of an economy already operating at its full productivity (on the PPF), which means that more of both outputs can now be produced during the specified period of time without sacrificing the output of either good. Conversely, the PPF will shift inward if the labour force shrinks, the supply of raw materials is depleted, or a natural disaster decreases the stock of physical capital.

However, most economic contractions reflect not that less can be produced but that the economy has started operating below the frontier, as typically, both labour and physical capital are underemployed, remaining therefore idle.

2. Demand curve and Supply curve

Demand curve, in economics, a graphic representation of the relationship between product price and the quantity of the product demanded. It is drawn with price on the vertical axis of the graph and quantity demanded on the horizontal axis. With few exceptions, the demand curve is delineated as sloping downward from left to right because price and quantity demanded are inversely related. This relationship is contingent on certain ceteris paribus (other things equal) conditions remaining constant. Such conditions include the number of consumers in the market, consumer tastes or preferences, prices of substitute goods, consumer price expectations, and personal income. A change in one or more of these conditions causes a change in demand, which is reflected by a shift in the location of the demand curve. A shift to the left indicates a decrease in demand, while a movement to the right an increase.

Supply curve, in economics, graphic representation of the relationship between product price and quantity of product that a seller is willing and able to supply. Product price is measured on the vertical axis of the graph and quantity of product supplied on the horizontal axis. In most cases, the supply curve is drawn as a slope rising upward from left to right, since product price and quantity supplied are directly related (i.e., as the price of a commodity increases in the market, the amount supplied increases). This relationship is dependent on certain ceteris paribus (other things equal) conditions remaining constant. Such conditions include the number of sellers in the market, the state of technology, the level of production costs, the seller’s price expectations, and the prices of related products. A change in any of these conditions will cause a shift in the supply curve. A shifting of the curve to the left corresponds to a decrease in the quantity of product supplied, whereas a shift to the right reflects an increase.

3. Market Equilibrium

In economics, economic equilibrium is a situation in which economic forces such as supply and demand are balanced and in the absence of external influences the (equilibrium) values of economic variables will not change. For example, in the standard textbook model of perfect competition, equilibrium occurs at the point at which quantity demanded and quantity supplied are equal. Market equilibrium in this case is a condition where a market price is established through competition such that the amount of goods or services sought by buyers is equal to the amount of goods or services produced by sellers. This price is often called the competitive price or market clearing price and will tend not to change unless demand or supply changes, and the quantity is called the “competitive quantity” or market clearing quantity. However, the concept of equilibrium in economics also applies to imperfectly competitive markets, where it takes the form of a Nash equilibrium.

4. Indifference Curve

Indifference curve, in economics, is a graph showing various combinations of two things (usually consumer goods) that yield equal satisfaction or utility to an individual. Developed by the Irish-born British economist Francis Y. Edgeworth, it is widely used as an analytical tool in the study of consumer behaviour, particularly as related to consumer demand. It is also utilized in welfare economics, a field that focuses on the effect of different actions on individual and general well-being.

The classic indifference curve is drawn downward from left to right and convex to the origin, so that a consumer who is given a choice between any two points on it would not prefer one point over the other. Because all of the combinations of goods represented by the points are equally desirable, the consumer would be indifferent to the combination actually received. An indifference curve is always constructed on the assumption that, other things being equal, certain factors remain constant.

An indifference curve connects points on a graph representing different quantities of two goods, points between which a consumer is indifferent. That is, the consumer has no preference for one combination or bundle of goods over a different combination on the same curve. One can also refer to each point on the indifference curve as rendering the same level of utility (satisfaction) for the consumer. In other words, an indifference curve is the locus of various points showing different combinations of two goods providing equal utility to the consumer. Utility is then a device to represent preferences rather than something from which preferences come. The main use of indifference curves is in the representation of potentially observable demand patterns for individual consumers over commodity bundles.

There are infinitely many indifference curves: one passes through each combination. A collection of (selected) indifference curves, illustrated graphically, is referred to as an indifference map. Indifferent curve is negatively sloped which means as quantity consumed of one good (X) increases, total satisfaction would increase if not offset by a decrease in the quantity consumed of the other good (Y). Indifference curves are convex to origin and do not intersect each other. If you move “off” an indifference curve traveling in a northeast direction (assuming positive marginal utility for the goods) you are essentially climbing a mound of utility. The higher you go the greater the level of utility. The non-satiation requirement means that you will never reach the “top,” or a “bliss point,” a consumption bundle that is preferred to all others.

5. Isoquant

An isoquant (derived from quantity and the Greek word iso, meaning equal) is a contour line drawn through the set of points at which the same quantity of output is produced while changing the quantities of two or more inputs. While an indifference curve mapping helps to solve the utility-maximizing problem of consumers, the isoquant mapping deals with the cost-minimization problem of producers. Isoquants are typically drawn along with isocost curves in capital-labor graphs, showing the technological tradeoff between capital and labor in the production function, and the decreasing marginal returns of both inputs. Adding one input while holding the other constant eventually leads to decreasing marginal output, and this is reflected in the shape of the isoquant. A family of isoquants can be represented by an isoquant map, a graph combining a number of isoquants, each representing a different quantity of output. Isoquants are also called equal product curves.

Production isoquant (strictly convex)  and isocost curve (linear)

An isoquant shows that extent to which the firm in question has the ability to substitute between the two different inputs at will in order to produce the same level of output. An isoquant map can also indicate decreasing or increasing returns to scale based on increasing or decreasing distances between the isoquant pairs of fixed output increment, as output increases. If the distance between those isoquants increases as output increases, the firm’s production function is exhibiting decreasing returns to scale; doubling both inputs will result in placement on an isoquant with less than double the output of the previous isoquant. Conversely, if the distance is decreasing as output increases, the firm is experiencing increasing returns to scale; doubling both inputs results in placement on an isoquant with more than twice the output of the original isoquant.

As with indifference curves, two isoquants can never cross. Also, every possible combination of inputs is on an isoquant. Finally, any combination of inputs above or to the right of an isoquant results in more output than any point on the isoquant. Although the marginal product of an input decreases as you increase the quantity of the input while holding all other inputs constant, the marginal product is never negative in the empirically observed range since a rational firm would never increase an input to decrease output.

An isoquants shows all those combinations of factors which produce same level of output. An isoquants is also known as equal product curve or iso-product curve. It describes the firm’s alternative methods for producing a given level of output.

6. Business Cycle- boom and bust

Business cycle refers to periodic fluctuations in the general rate of economic activity, as measured by the levels of employment, prices, and production. The business cycle, also known as the economic cycle or trade cycle, is the downward and upward movement of gross domestic product (GDP) around its long-term growth trend. The length of a business cycle is the period of time containing a single boom and contraction in sequence. These fluctuations typically involve shifts over time between periods of relatively rapid economic growth (expansions or booms) and periods of relative stagnation or decline (contractions or recessions).

Business cycles are usually measured by considering the growth rate of real gross domestic product. Despite the often-applied term cycles, these fluctuations in economic activity do not exhibit uniform or predictable periodicity. The common or popular usage boom-and-bust cycle refers to fluctuations in which the expansion is rapid and the contraction severe.

In 1860 French economist Clément Juglar first identified economic cycles 7 to 11 years long, although he cautiously did not claim any rigid regularity. Later, economist Joseph Schumpeter (1883–1950) argued that a Juglar cycle has four stages:

• Expansion (increase in production and prices, low interest-rates)
• Crisis (stock exchanges crash and multiple bankruptcies of firms occur)
• Recession (drops in prices and in output, high interest-rates)
• Recovery (stocks recover because of the fall in prices and incomes)

Schumpeter’s Juglar model associates recovery and prosperity with increases in productivity, consumer confidence, aggregate demand, and prices.

In the 20th century, Schumpeter and others proposed a typology of business cycles according to their periodicity, so that a number of particular cycles were named after their discoverers or proposers:

In the 20th century, Schumpeter and others proposed a typology of business cycles according to their periodicity, so that a number of particular cycles were named after their discoverers or proposers:

• The Kitchin inventory cycle of 3 to 5 years (after Joseph Kitchin)
• The Juglar fixed-investment cycle of 7 to 11 years (often identified as “the” business cycle
• The Kuznets infrastructural investment cycle of 15 to 25 years (after Simon Kuznets – also called “building cycle”)
• The Kondratiev wave or long technological cycle of 45 to 60 years (after the Soviet economist Nikolai Kondratiev)

Some say interest in the different typologies of cycles has waned since the development of modern macroeconomics, which gives little support to the idea of regular periodic cycles.

7. Inflationary and deflationary Gap

The inflationary gap exists when the demand for goods and services exceeds production due to factors such as higher levels of overall employment, increased trade activities or increased government expenditure. This can lead to the real GDP exceeding the potential GDP, resulting in an inflationary gap. The inflationary gap is so named because the relative increase in real GDP causes an economy to increase its consumption, which causes prices to rise in the long run.

The inflationary gap is always an ex-ante phenomenon; it is always expected to occur in the future. It arises when expected expenditure will not equal expected consumption at a future date.Keynes defines it as the excess demand in the market for consumption of goods and services. He defined an inflationary gap as an excess of planned expenditure over the available output at pre-inflation or base prices. Given a constant average propensity to save; rising money incomes at full employment level would lead to an excess of demand over supply and to a consequent inflationary gap. Thus Keynes used the concept of the inflationary gap to show the main determinants that cause an inflationary rise of prices.

 When the potential GDP is higher than the real GDP, the gap is referred to as a deflationary gap. Deflationary gap is the difference between potential output at full level of employment and the actual level of output of the economy. For deflationary gap all the resources of the economy are not being used to the optimum level and some are idle.  This comes with unemployment and low levels of output.

8. Phillips Curve

Phillips curve is a graphic representation of the economic relationship between the rate of unemployment (or the rate of change of unemployment) and the rate of change of money wages. Named for economist A. William Phillips, it indicates that wages tend to rise faster when unemployment is low. In “The Relation Between Unemployment and the Rate of Change of Money Wage Rates in the United Kingdom, 1861–1957” (1958), Phillips found that, except for the years of unusually large and rapid increases in import prices, the rate of change in wages could be explained by the level of unemployment. Simply put, a climate of low unemployment will cause employers to bid wages up in an effort to lure higher-quality employees away from other companies. Conversely, conditions of high unemployment eliminate the need for such competitive bidding; as a result, the rate of change in paid compensation will be lower.

The main implication of the Phillips curve is that, because a particular level of unemployment will influence a particular rate of wage increase, the two goals of low unemployment and a low rate of inflation may be incompatible. Developments in the United States and other countries in the second half of the 20th century, however, suggested that the relation between unemployment and inflation is more unstable than the Phillips curve would predict. In particular, the situation in the early 1970s, marked by relatively high unemployment and extremely high wage increases, represented a point well off the Phillips curve. At the beginning of the 21st century, the persistence of low unemployment and relatively low inflation marked another departure from the Phillips curve.

While there is a short run tradeoff between unemployment and inflation, it has not been observed in the long run. In 1967 and 1968, Milton Friedman and Edmund Phelps asserted that the Phillips curve was only applicable in the short-run and that in the long-run, inflationary policies would not decrease unemployment.  Friedman then correctly predicted that in the 1973–75 recession, both inflation and unemployment would increase. The long-run Phillips curve is now seen as a vertical line at the natural rate of unemployment, where the rate of inflation has no effect on unemployment.

9. J- Curve

In economics, the ‘J curve’ is the time path of a country’s trade balance following a devaluation or depreciation of its currency, under a certain set of assumptions. A devalued currency means imports are more expensive, and on the assumption that the volumes of imports and exports change little at first, this causes a fall in the current account (a bigger deficit or smaller surplus). After some time, though, the volume of exports may start to rise because of their lower and hence more competitive prices to foreign buyers and domestic consumers may buy fewer of the costlier imports. Eventually, if this happens, the trade balance should move to a smaller deficit or larger surplus compared to what it was before the devaluation. Likewise, if there is a currency revaluation or appreciation the same reasoning may be applied and will lead to an inverted J curve.

Immediately following the depreciation or devaluation of the currency, the total value of imports will increase and exports remain largely unchanged due in part to pre-existing trade contracts that have to be honored. This is because in the short run, prices of imports rise due to the depreciation and also in the short run there is a lag in changing consumption of imports, therefore there is an immediate jump followed by a lag until the long run prevails and consumers stop importing as many expensive goods and along with the rise in exports cause the current account to increase (a smaller defect or a bigger surplus). Moreover, in the short run, demand for the more expensive imports (and demand for exports, which are cheaper to foreign buyers using foreign currencies) remain price inelastic. This is due to time lags in the consumer’s search for acceptable, cheaper alternatives (which might not exist).

Over the longer term depreciation in the exchange rate can have the desired effect of improving the current account balance. Domestic consumers might switch their expenditure to domestic products and away from expensive imported goods and services, assuming equivalent domestic alternatives exist. Equally, many foreign consumers may switch to purchasing the products being exported into their country, which are now cheaper in the foreign currency, instead of their own domestically produced goods and services.

Empirical investigations of the J curve have sometimes focused on the effect of exchange rate changes on the trade ratio, i.e. exports divided by imports, rather than the trade balance, exports minus imports. Unlike the trade balance, the trade ratio can be logarithmically transformed regardless of whether a trade deficit or trade surplus exists.

10. Laffer Curve

The Laffer Curve is a theory developed by supply-side economist Arthur Laffer to show the relationship between tax rates and the amount of tax revenue collected by governments. The curve is used to illustrate Laffer’s argument that sometimes cutting tax rates can increase total tax revenue. The Laffer Curve describes the relationship between tax rates and total tax revenue, with an optimal tax rate that maximizes total government tax revenue.

If taxes are too high along the Laffer Curve, then they will discourage the taxed activities, such as work and investment, enough to actually reduce total tax revenue. In this case, cutting tax rates will both stimulate economic incentives and increase tax revenue. The Laffer Curve was used as a basis for tax cuts in the 1980’s with apparent success, but criticized on practical grounds on the basis of its simplistic assumptions, and on economic grounds that increasing government revenue might not always be optimal.

The Laffer Curve is based on the economic idea that people will adjust their behavior in the face of the incentives created by income tax rates. Higher income tax rates decrease the incentive to work and invest compared lower rates. If this effect is large enough, it means that at some tax rate, and further increase in the rate will actually lead to decrease in total tax revenue. For every type of tax, there is a threshold rate above which the incentive to produce more diminishes, thereby reducing the amount of revenue the government receives.

At a 0% tax rate, tax revenue would obviously be zero. As tax rates increase from low levels, tax revenue collected by the also government increases. Eventually, if tax rates reached 100 percent, shown as the far right on the Laffer Curve, all people would choose not to work because everything they earned would go to the government. Therefore it is necessarily true that at some point in the range where tax revenue is positive, it must reach a maximum point. This is represented by T* on the graph below. To the left of T* an increase in tax rate raises more revenue than is lost to offsetting worker and investor behavior. Increasing rates beyond T* however would cause people not to work as much or not at all, thereby reducing total tax revenue.

Therefore at any tax rate to the right of T*, a reduction in tax rate will actually increase total revenue. The shape of the Laffer Curve, and thus the location of T* is dependent on worker and investor preferences for work, leisure, and income, as well as technology and other economic factors. Governments would like to be at point T* because it is the point at which the government collects maximum amount of tax revenue while people continue to work hard. If the current tax rate is to the right of T*, then lowering the tax rate will both stimulate economic growth by increasing incentives to work and invest, and increase government revenue because work and investment means a larger tax base.

11. Engel’s Curve

In microeconomics, an Engel curve describes how household expenditure on a particular good or service varies with household income. There are two varieties of Engel curves. Budget share Engel curves describe how the proportion of household income spent on a good varies with income. Alternatively, Engel curves can also describe how real expenditure varies with household income. They are named after the German statistician Ernst Engel (1821–1896), who was the first to investigate this relationship between goods expenditure and income systematically in 1857. The best-known single result from the article is Engel’s law which states that the poorer a family is, the larger the budget share it spends on nourishment.

Graphically, the Engel curve is represented in the first quadrant of the Cartesian coordinate system. Income is shown on the Y-axis and the quantity demanded for the selected good or service is shown on the X-axis. The shapes of Engel curves depend on many demographic variables and other consumer characteristics. A good’s Engel curve reflects its income elasticity and indicates whether the good is an inferior, normal, or luxury good. Empirical Engel curves are close to linear for some goods, and highly nonlinear for others.

For normal goods, the Engel curve has a positive gradient. That is, as income increases, the quantity demanded increases. Amongst normal goods, there are two possibilities. Although the Engel curve remains upward sloping in both cases, it bends toward the X-axis for necessities and towards the Y-axis for luxury goods.

For inferior goods, the Engel curve has a negative gradient. That means that as the consumer has more income, they will buy less of the inferior good because they are able to purchase better goods. For goods with a Marshallian demand function generated from a utility function of Gorman polar form, the Engel curve is a straight line.

Many Engel curves feature saturation properties in that their slope tends toward infinity at high income levels, which suggests that there exists an absolute limit on how much expenditure on a good will rise as household income increases.This saturation property has been linked to slowdowns in the growth of demand for some sectors in the economy, causing major changes in an economy’s sectoral composition to take place.