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Cobweb theorem as an illustration of stable and unstable equilibrium

Cobwebis a simple model used to illustrate the danger that time lags may introduce fluctuations into the economy. This simple dynamic model of cyclical demand with time lags between the response of production and a change in price (most often seen in agricultural sectors). Cobweb theory is the process of adjustment in markets.

It traces the path of prices and outputs in different equilibrium situations. Path resembles a cobweb with the equilibrium point at the center of the cobweb.


– have a perfectly competitive market

– production period is long

– the price is determined by contemporary production

– quantity supplied is determined by contemporary price

Model can be illustrated with the help of the following graphs: Stable cobweb

EXPLANATION: Assume that this represents the market for X-good. The current price is Pe and quantity bought and sold Qe.

Assume that prise rises from Pe to P1. At the current market price of Pe there will be a surplus created – buyers cannot easily increase the demand of X-good in the short run. This would cause the price to fall (P2). The lower price encourages consumers to buy more goods – the damand at the end of the period will increase to Q2.

The increased demand at a price of P2 however is met with a reduction in quantity supplied. It means that there is shortage in the market. As a result the price increases to P3 level.

The higher price persuades produsers to increase production quantity for the next period (Q4).

At P3 the lower demand means a surplus is created press the price down to P4. This will encourage buyers to expand consumption to Q4.

This process will continue until the price reaches equilibrium. This is termed a ‘convergent cobweb’.A convergent cobweb leads to price stability over time.


Unstable cobweb

Constant cobweb

Date: 2016-03-03; view: 2960

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