Crye, 907 S.W.2d at 500. Reasonable probability is determined by the substance and context of the opinion and does not turn on semantics or on the use of a particular term or phrase. Id.; Myers, 411 S.W.2d at 713. An expert must base his opinion on facts or data perceived or reviewed during or before trial. Tex.R. Evid. 703; Onwuteaka v. Gill, 908 S.W.2d 276, 283 (Tex.App.-Houston [1st Dist.] 1995, no writ). The weakness of facts in support of an expert’s opinion generally goes to the weight of the testimony rather than the admissibility. Onwuteaka, 908 S.W.2d at 283. Nevertheless, an expert’s opinion regarding causation that is based completely upon speculation and surmise amounts to no evidence. Id.; see also Schaefer v. Tex. Employers’ Ins. Ass’n, 612 S.W.2d 199, 204-05 (Tex.1980) (<HOLDING>). “If the foundational data underlying opinion
holding that a medical opinion is adequate where it is based upon the veterans medical history examinations and the also describes the disability in sufficient detail holding that the plaintiffs experts were not qualified to offer a medical opinion as to the cause of death because they are not physicians nor otherwise properly qualified to offer a medical opinion holding that experts medical opinion constituted no evidence because it was based upon speculation and surmise rather than reasonable medical probability holding a finding of fact by the commission may not be based upon surmise conjecture or speculation but must be founded on evidence of sufficient substance to afford a reasonable basis for it holding expert testimony provided no evidence as to causation since testimony was not based upon reasonable medical probability