In this asbestos injury suit, the appellants challenge the district court’s grant of partial summary judgment, arguing that the court improperly assessed the credibility of their expert witnesses. Finding that *306 the district court acted within its authority in evaluating the reliability of this evidence, we affirm.
Facts and District Court Proceedings
The 451 plaintiffs in this action are members of the National Rubber Workers Union. Through the efforts of the National Tire Workers Litigation Project, these workers participated in diagnostic screenings to detect the presence of asbestos-related disease. These screenings, conducted in mobile units, consisted of X-rays and workplace questionnaires completed by the workers. The screenings did not include physical examinations.
After two years of discovery, the appel-lees filed a motion for partial summary judgment accompanied by 310 pages of X-ray examination reports and the affidavit of the appellees’ pulmonary specialist, Dr. Bradley. Bradley’s affidavit stated his conclusion that based upon his review of the X-rays and reports attached as exhibits, 421 plaintiffs showed no signs of pulmonary disease. In reply, the appellants submitted the affidavits of their pulmonary specialists, Drs. Gelbard and Rao. Although these affidavits referenced the X-rays, questionnaires, and examination reports as exhibits, these items were never submitted as summary judgment evidence.
At the hearing on the summary judgment motion, the appellees identified several inconsistencies between the examination reports and the conclusions later reached by the appellant’s experts. 1 Disturbed by the district judge's comments at the end of the hearing, the appellants submitted additional affidavits from other experts. The court refused to consider this proffer, characterizing those affidavits as “uninvited and untimely.” The trial court granted the appellees’ motion for summary judgment, which was later certified as a final judgment. This appeal followed.
The Requirements of Rule 703
The appellants argue that in granting the summary judgment motion, the district court improperly judged the credibility of their expert witnesses, a function typically within the purview of the jury. 2 Because the diagnostic methods employed by the appellants’ experts are widely accepted in the medical community, the appellants argue that the jury should have been permitted to hear and evaluate the evidence. We are unpersuaded.
As a general rule, questions regarding the scientific bases of an expert’s opinion “affect the weight to be assigned that opinion rather than its admissibility and should be left for the jury’s consideration.”
Viterbo v. Dow Chemical Co.,
The “sources” of the experts’ opinions were the examination reports previously compiled. As the appellees demonstrated at the summary judgment hearing, a sampling of these reports revealed that they were replete with “so many obvious errors as to be of no value to the trier of fact.” Additionally, although the affidavit referenced the reports as exhibits, they were never submitted as summary judgment evidence.
4
Considering these inadequacies, the Gelbard and Rao affidavits represented nothing more than bare conclusions derived from erroneous data. As this court noted in
Viterbo,
“[wjithout more than credentials and a subjective opinion, an expert’s opinion that ‘it is so’ is not admissible.”
Viterbo,
The Post-Hearing Affidavits
The appellants contend that the district court erred in refusing to accept additional supporting affidavits filed after the summary judgment hearing. We disagree.
Under Federal Rule of Civil Procedure 6(b), the trial court has broad discretion to accept late-filed affidavits “where the failure to act was the result of excusable neglect.” Absent an affirmative showing of excusable neglect, a trial court does not abuse its discretion in refusing an untimely proffer.
Bernhardt v. RichardsonMerrell, Inc.,
The appellants have made no such showing of excusable neglect. The record reflects that the late-filed affidavits were prepared long before the summary judgment motion was filed. The appellants made a tactical decision to withhold them because they were fatal to the claims of many of the plaintiffs. We find this tactical decision inequivalent to the “excusable neglect” demonstrated by the plaintiff in
Littlejohn v. Shell Oil Co.,
Conclusion
For the foregoing reasons, the judgment of the district court is
AFFIRMED.
Notes
. The appellees noted that the workplace questionnaires completed by the workers were often inconsistent with the information contained in the experts’ examination report. For example, an illustrative questionnaire contained the following responses:
£ If |c?
Have you worked close to lined “hot pipes"? X
Have you worked with or close to:
Soapstone? Talcum powder? Asbestos? XXX
In spite of this information, Dr. Gelbard states in her examination report:
"He worked ... with asbestos, soapstone, talc, and close to hot pipes ... During that period he noted exposures to thermal insulation and other asbestos-containing products."
. As the appellant properly argues, a district court may not base a decision to admit expert testimony upon its assessment of the credibility of the expert.
Honore v. Douglas,
. Federal Rule of Evidence 703 establishes the parameters for expert testimony. Under the rule, an expert may base his opinion on facts or data perceived by him or others, including otherwise inadmissible facts, if those facts are "of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject_” See,
Soden,
. We reject the appellant’s argument, based upon
Bulthuis v. Rexall Corp.,
.We distinguish this case from
Christophersen v. Allied-Signal Corp.,
