This slide deck from the IMF has some numbers on audits and liabilities found that could help form a ballpark estimate of the amount of non-compliance in Malaysia (the issue with these numbers being that they aren't random audits as are typically used to determine the tax gap).
This dissertation (from 2001) finds that compliance with the personal income tax in Malaysia is about 52%.
This slide deck from the IMF has some numbers on audits and liabilities found that could help form a ballpark estimate of the amount of non-compliance in Malaysia (the issue with these numbers being that they aren't random audits as are typically used to determine the tax gap).
This dissertation (from 2001) finds that compliance with the personal income tax in Malaysia is about 52%.