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One of the basic assumptions of asset pricing models (CAPM and APT) is the efficiency of markets. This paper seeks to prove this requirement in its weak form, both for the General Index of the Stock Exchange of Colombia and for the Colombian market's most representative assets. To this end, different statistical methods are implemented to show that stock patterns do not follow a normal distribution pattern. Additionally, when testing the Colombian efficiency market through a series of runs, BDS, LB and Bartlett test, there is no evidence of randomness in the main financial assets except Ecopetrol. Moreover, in the specific case of IGBC there is an improvement in market efficiency from 2008 to 2010, period that coincides with the onset of the global economic crisis. [ABSTRACT FROM AUTHOR]

In this paper we analyze the historical returns of the companies listed on the Colombian stock exchange, from January 2004 until June 2012, in order to determine the possible presence of a risk premium in smaller companies relative to larger ones. This premium is known as Size Effect and it has been found that it is significant after adjusting of risk by Capital Asset Pricing Model. The results obtained in this work for the stock market in Colombia do not show the presence of an additional risk premium due to the size of enterprises, rejecting both size effect and reverse size effect. [ABSTRACT FROM AUTHOR]