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. [Citation.] (Jones v. Ortho Pharmaceutical Corp. (1985) 163 Cal.App.3d 396, 402-403, 209 Cal.Rptr. 456.)

[239 Cal.App.4th 578]