In financial markets, the symmetry of information and the homogeneous interpretation of information among traders is one of the main conditions for market efficiency, but these conditions are in fact violated. In this paper first; we accurately estimated the dynamic measures of trades stemming from information asymmetry and diverse opinions among investors indices by a hidden Markov model. Thereafter, we consider an event window of 21 days to investigate impact of information disclosure on that indices. For this purpose, we estimated the daily measures of probability of informed trading (PIN) and symmetric-order flow shock (PSOS) 32 Tehran Stock Exchange (TSE) stocks belonging to 11 industries of TSE during the period from 2015 to 2018. PIN is an indicator of asymmetric information risk and PSOS indicating diverse opinions among investors whose variations and intensity play an important role in price formation and stock liquidity. These results show that in most stocks that have higher market value experience less risks of asymmetric information and diverse opinions shocks than other stocks. Entirely, it appears that the average and the maximum of information risk and diverse opinions shocks at TSE are higher than in developed markets. Also, information disclosure decreases PIN for three days and increases PSOS for 10 days, significantly, but its impact on PIN is weaker than PSOS. Actually, in TSE, information advantage of some informed traders are independent of announcements as well as announcements causes opinion diversities to rise and stand up.
