What is the test for establishing causation in a personal injury action?

"The law is well settled that in a personal injury action causation must be proven within a reasonable medical probability based upon competent expert testimony. Mere possibility alone is insufficient to establish a prima facie case. [Citations.] That there is a distinction between a reasonable medical 'probability' and a medical 'possibility' needs little discussion. There can be many possible 'causes,' indeed, an infinite number of circumstances which can produce an injury or disease. A possible cause only becomes 'probable' when, in the absence of other reasonable causal explanations, it becomes more likely than not that the injury was a result of its action. This is the outer limit of inference upon which an issue may be submitted to the jury." (Jones v. Ortho Pharmaceutical Corp. (1985) 163 Cal.App.3d 396, 402-403.)