“…Concentration on the market of auditing services can also be measured by the market share of the BIG4 companies, i.e., PricewaterhouseCoopers, Deloitte, KPMG, and Ernst & Young [Financial Reporting Council, 2010;Indyk, 2019] and using the "10KAP" ratio, which means the share of the ten key audit companies in the audit market, i.e., Baker Tilly; BDO; Ernst & Young; Deloitte; Grant Thornton; KPMG; Mazars; Moore Stephens; Nexia; and PricewaterhouseCoopers [European Commission, 2017]. In the study prepared by the OECD [1993], it is recommended to use two indices to study the concentration on the audit services market, i.e., CR k and HHI, of which the CR k index is most often used in the literature [Mijic et al, 2014;Paunescu, 2015;Malis and Brozovic, 2015;Groff and Salihovic, 2016;European Commission, 2017, 2021. The CR k ratio means the consolidated market share of the k largest audit firms.…”