First, if there is no test.

Second, the elimination method.

Third, the substitution method.

Fourth, the presumption rule of causality.

Legal basis: Article 54 of the Provisions on Procedures for Handling Road Traffic Accidents, an appraisal institution shall complete the inspection and appraisal within the prescribed time limit, and issue a written inspection report and appraisal opinion, which shall be signed by the appraiser, and the appraisal opinion shall also be stamped with the seal of the institution. The inspection report and appraisal opinions shall specify the following items:

(1) Principal (2) Entrusting date and matters (3) Relevant materials submitted (4) Inspection and appraisal time (5) Basis and conclusive opinions. If a conclusive opinion is reached through analysis, there should be an analysis and demonstration process.

The inspection report and appraisal opinions shall be accompanied by the qualification certificates or other supporting documents of the appraisal institutions and appraisers.