Towards unbiased portfolio daily returns

This paper describes a new method to generate unbiased equal-weighted portfolio daily returns by removing the impacts of bid-ask bounce and non-synchronous trading. For example, for the CRSP daily equal-weighted market index over 1964 to 1993 (EWRETD), the annual bias of the time series generated by our method is 0.05%, considerably smaller than 6% as reported by Canina et al. (1998). In addition, we also discuss the research impact by using both biased and unbiased daily EWRETD on beta, alpha, volatility and event study. The paper concludes that the new method should be applied for future estimation of portfolio daily returns which can be either equal-weighted or value-weighted.