Bandid Nijathaworn, president and CEO of the institute, said that the ranking is based on publicly-disclosed information.
"The board of directors should have clear policy on inside information which strictly binds all in the organisations. What happened is an example that the board of directors must strictly enforce the policy," he said.
The institute's ranking announced recently was based on the information disclosed during January 1, 2014 through October 19, 2015.
His comment followed the Securities and Exchange Commission's announcement on December 2 that four individuals were fined for using inside information in buying shares of Siam Makro.
They are Korsak Chairasmisak, Piyawat Titasattavorakul and Pittaya Jearavisitkul who are directors of CP All. Athueck Asvanund, vice chairman of True Corp, was also fined. The SEC's Settlement Committee fined the four for Bt33.33 million.
The committee also fined Somsak Chiarawisithkul and Areeya Asvanund for Bt333,333.33 for aiding and abetting in the deal.
According to the SEC, the four directors bought the shares during April 10-22, 2013 when CP All was in negotiation with SHV Netherland B.V. (SHV) to purchase 154,429,500 shares or 64.35 percent of the total ordinary shares of MAKRO.
The misconducts committed by Korsak, Pittaya, Piyawat and Athueck were liable to violation of Section 241 of the Securities and Exchange Act (SEA) BE 2535, the SEC announced.
All of the six individuals above had agreed to enter the settlement process. The Settlement Committee consequently fined Korsak at the amount of Bt30 million, Athueck Bt1.4 million, Pittaya Bt979,500, and Piyawat Bt725,000.