In attempting to identify bubbles before they burst, economists have developed a number of financial ratios and economic indicators that can be used to evaluate whether homes in a given area are fairly valued. By comparing current levels to previous levels that have proven unsustainable in the past (i.e. led to or at least accompanied crashes), one can make an educated guess as to whether a given real estate market is experiencing a bubble. Indicators describe two interwoven aspects of housing bubble: a valuation component and a debt (or leverage) component. The valuation component measures how expensive houses are relative to what most people can afford, and the debt component measures how indebted households become in buying them for home or profit (and also how much exposure the banks accumulate by lending for them).