## Facts

- Albert Roy Christophersen worked about 14 years for a manufacturer of nickel-cadmium batteries and was allegedly exposed to workplace fumes.
- He died in 1986 from a rare metastatic colon cancer.
- His surviving spouse and child sued the employer and multiple suppliers under Texas wrongful death and survival law, alleging defective products caused toxic fumes containing nickel and cadmium that caused his cancer.
- Plaintiffs’ causation proof depended primarily on one medical expert, an oncologist (Dr. Miller), who opined that nickel/cadmium exposure caused the cancer.
- Dr. Miller relied on medical records and a coworker affidavit describing fumes and conditions; the coworker did not know the fumes’ chemical composition.
- Dr. Miller assumed a 20-year exposure period despite an employment record of 14 years and relied on scientific literature involving materially different exposure conditions (including high-dose animal studies).

## Issues

1. What standard governs admissibility of expert scientific causation testimony in a toxic-tort case under Federal Rules of Evidence 702 and 703, including assessment of the opinion’s factual and methodological basis?
2. Whether the district court abused its discretion by excluding Dr. Miller’s causation testimony under Rules 702/703 and alternatively Rule 403, resulting in summary judgment for defendants.

## Decision

- The en banc Fifth Circuit affirmed the exclusion of Dr. Miller’s expert testimony and affirmed summary judgment for all defendants.
- The court held the district judge acted within discretion in finding the opinion’s factual predicates and reasoning too weak and speculative to assist the jury.
- The court agreed that, given the minimal probative value and risk of misleading the jury, exclusion under Rule 403 was also within the trial court’s discretion.
- With the sole causation expert excluded, plaintiffs lacked admissible evidence on an essential element, making summary judgment proper.

## Legal Principles

- Trial courts must screen expert testimony for reliability and helpfulness; an expert opinion that is fundamentally unsupported by adequate facts or data provides no assistance to the jury and may be excluded.
- Under Rule 703, an expert’s bases must be of a type reasonably relied upon by experts in the field; speculative assumptions about exposure content, dose, or duration can render an opinion inadmissible.
- Courts may examine whether the scientific materials and reasoning logically support the expert’s conclusion as a threshold admissibility question, not merely a question of weight.
- Rule 403 permits exclusion of expert testimony when weakly supported scientific opinions risk undue prejudice or jury confusion because scientific testimony can carry disproportionate persuasive force.
- Appellate review of expert-admissibility rulings is for abuse of discretion; once excluded, absence of admissible proof on causation can justify summary judgment.

## Conclusion

The Fifth Circuit upheld rigorous judicial control over toxic-tort causation testimony, affirming exclusion of an expert opinion resting on unreliable exposure assumptions and weak scientific support; without that evidence, plaintiffs could not create a genuine fact dispute on causation and defendants were entitled to summary judgment.


Christophersen v. Allied-Signal Corp., 939 F.2d 1106 (5th Cir. 1991) (en banc)