Let assume that the value of the stock in a firm depends on observable signal (s),and unobserved random variable (e).Thus ,the value of the stock is given by v= s + e. Therefore the effective (expected) price is p = v .The better the signal the higher, the price. Besides, price itself must include all the information available.
Now consider a market with two types of investors: well informed and uniformed ones. Those uniformed investors , keep attention on prices to get the signal they need. In such a case, the market itself provide all the information about the value of the stock and its equilibrium range.(Varian ,1978).-
The problem arises because it is costly to get those signal, and the rating agencies have the task of reducing that cost .So, informed investor will pay the price (hiring financial advisers, consultants ,lawyers, accountants ), but , uniformed investor, who I assume do not have the same capability to get information on their own, depend upon the rating agency to make the proper decision. This heterogeneity ,will lead to information asymmetry with not market efficient equilibrium, as long rating agency on the other side has a profit seeking strategy which is a quite different goal , respect to the one most important for investors: to provide risk evaluation.-
Whether the rating agencies fool or mislead uninformed investors, the outcome will be inefficient allocation of resources ,because their portfolio will have riskier assets, than the investors consider representative of their preferences for assets risk . As a result, market might get into a risk bubble whose final outcome is not other than downward price adjustment once it burst, and both the investors and banks which support them with finance assistance , end up worse off. The raring agencies, might not be in such a trouble , given the fact that they manage a variety of portfolios none all of them equally risky.-
The insurance industry, is also a good example about the implication of information asymmetry .When a customer get an insurance for theft bikes ,the company has no way to make sure that the customer will behave properly to avoid his /her bike, to be stolen afterward the insurance has been signed up. As a result, the insurance company find itself losing money. In this case, to avoid such a loses ,insurance company offer deductible policies .Consumers pay a share of their insurance, which induce them to have a more cautious behaviour .However, what is it the optimal level of care on personal behaviour? .If consumer get too cautious, it is not worth to waste money with insurance programs , and on the contrary if it get too risky, there is no cost free insurance policy. Thus ,even with an average behaviour consumer end up worse off because they end up paying for higher risk than they effectively engage on.-
What all of this means ?. It is not impossible to prevent bubbles developing and its outcome , as long as there is information asymmetry among market players which is not corrected at the right time .Thus, to avoid such outcome, it is important to have the proper institutional setting to make sure that information asymmetry does not mean a systemic risk threat. This consciousness, will imply regular oversight about the risk level the system is undertaking. It follows, that full information about the quality of assets involved ,is key on this approach as much as it is necessary a review of Basel II accord.-