A social insurance scheme is an insurance scheme where the following two conditions are satisfied, (a) the benefits received are conditional on participation in the scheme and constitute social benefits as this term is used in the SNA, and (b) at least one of the three conditions following is met.
(Ⅰ) Participation in the scheme is obligatory either by law or under the terms and conditions of employment of an employee, or group of employees.
(ⅠⅠ) The scheme is a collective one operated for the benefit of a designated group of workers, whether employed or non-employed, participation being restricted to members of that group.
(ⅠⅠⅠ) An employer makes a contribution (actual or imputed) to the scheme on behalf of an employee, whether or not the employee also makes a contribution.

System of National Accounts 2008