According to the 1993 SNA, two factors determine whether a corporation or non-profit institution is controlled by government and thus falls into the public sector. One factor is the degree of control exercised by government. Concern has been expressed about the "mainly financed" phrase cited in respect of non-profit institutions. The determination of control in respect of special purpose vehicles (SPVs), notably created in the context of public private partnerships (PPPs) or securitization, is not always clear cut. The second factor is about "economically significant prices." Concern has also been expressed over possible ambiguity in this concept. Is it possible to give greater content to the description without going so far as to prescribe a fixed proportion of costs to be covered by sales?