The Stock Market is affected by a combination of fundamental, easily quantifiable factors, yet at the same time, it is greatly affected by psychological and social factors that are not easily quantifiable. Many model have attempted to represent the actual data and trends observed over different time periods, however there is no model to date that sufficiently describes the movements of Stock Prices and the Volatility of the Stock Market.
Behavioral Finance is a developing field of study, but promises to give significant insights into the behavior of the stock market and may, in time give rise to a more accurate model.