摘要：This paper presents an empirical investigation to study the relationship between product market competition and voluntary disclosure among 124 selected firms listed on Tehran Stock Exchange over the period 2004-2013. The study uses Herfindahl–Hirschman Index (HHI) and Lerner (LLIA) index to measure competition in terms of capacity and price, respectively. In addition, the study uses the questionnaire developed by Botosan (1997) [Botosan, C. A. (1997). Disclosure level and the cost of equity capital. Accounting Review, 72(3), 323-349.] to measure voluntary disclosure. Using linear regression technique, the study has determined that there was a meaningful, direct and positive relationship between voluntary disclosure and competition in terms of price (LLIA). In addition, the results indicate that there was a meaningful and reverse relationship between voluntary disclosure and competition in terms of capacity (HHI).
