dissenting.
This court has now, for the second time, set aside a multi-million dollar verdict for the plaintiff and has ordered the case to be tried for a third time. It does so, in my judgment, on a remarkably insubstantial basis and one utterly unsupported by the law or the facts of the case.
The principal reason assigned for invalidating the jury’s verdict is that the testimony of the plaintiffs expert witness as to the requirements for diligent mining was “too speculative to be admissible.” I respectfully disagree.
The majority opinion holds that the trial judge erred in receiving, over the defendant’s objection, the expert opinion testimony of plaintiff’s witness, Mr. Barker. A careful reading of the court’s opinion reveals that it actually challenges Mr. Barker’s opinion on two grounds: 1) that many of the witness’s assumptions such as the quality of the coal involved, potential available sales prices, possible production problems, and the capacity of a certain coal washing facility, are incorrect, and 2) that the witness’s opinion does not establish the proper measure of damages that should result from a diligent mining plan because “he acknowledged that although his plan provided for mining 400,000 tons of coal a year, 250,000 or 300,000 could also be considered diligent.” P. 771.
The short answer to the two contentions made in the majority opinion is that the first is no more than a disagreement with the data base upon which the acknowledged expert rested his opinion and is a matter exclusively within the province of the jury, and the second is simply a mistaken understanding of the evidence.
The majority acknowledges that Mr. Barker was qualified as an expert to render an opinion about the matter for which he was called to testify — his opinion, as an experienced coal producer, as to what a plan for the diligent mining of the property required. He gave that opinion and, in doing so, testified at length about the data upon which his opinion rested. He emphasized that his opinion of what diligent mining of the property required was not measured entirely by the amount of coal that would be produced for a given period of mining. Many other factors, he said, comprised his opinion of what diligent mining of the property required. The majority opinion takes issue, however, with the sufficiency of the factual basis for Mr. Barker’s opinion, disagrees with the significance of the factors he relied upon, points to considerations my colleagues think important that Mr. Barker did not, argues that the diligent mining plan described by the witness is deficient, and concludes therefrom that the witness’s testimony is inadmissible mere speculation.
Federal Rule of Evidence 703 provides:
The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. i
In explicating its understanding of Rule 703, this court has stated:
The purpose of Rule 703 is to make available to the expert all of the kinds of things that an expert would normally rely upon in forming an opinion, without requiring that these be admissible in evidence. Under the Rule, the expert is free to give his opinion relying upon the types of data an expert would normally use in forming an opinion in his area of expertise.
Mannino v. International Mfg. Co., 650 F.2d 846, 851 (6th Cir.1981).
Although defendant G & W argues, and my colleagues agree, that the plaintiff’s expert testimony is speculative, neither suggest that Mr. Barker was not relying on data of a type reasonably relied upon by experts in his field. The court holds that *778Mr. Barker’s opinion should not have been considered by the jury because the opinion did not take into account factors the court regards as critical to a valid diligent mining opinion. For example, the majority holds that the coal prices used by Mr. Barker in his diligent mining plan were purely speculative. The expert testified, however, that he verified the selling price by checking pricing schedules used by other coal companies which were in effect at the time the plan was to be effective. My colleagues do not argue that an expert in the field may not reasonably rely on such data. They hold instead that the defendant did not sell the coal for the price Mr. Barker claimed it could be sold for, and that Mr. Barker did not “take into account any down time or any unusual problems because of the size or width of the seams, delay in availability of freight cars, or any other of the actual problems that were actually encountered in mining the leases.” I am unable to see how Mr. Barker’s disagreement with the witness Meadows that the coal was sixty percent metallurgical and forty percent steam, his failure to testify that sometimes coal is sold through brokers who receive six to nine percent commissions, and his assumptions that the coal could be sold at prices with which the defendant disagreed, renders his opinion inadmissible. The court also objects to Mr. Barker’s determinations about the coal market, mining costs, contracting costs, and the quality and quantity of the coal contained in the lease properties. But all of these factors were components of his diligent mining plan and comprised the data base upon which his opinion rested. The witness testified that he verified all the figures used as a basis for making his determinations, and that his plan was developed in accordance with generally accepted mining principles. The court’s opinion that the data the expert relied upon in forming his expert opinion was inadequate, irrelevant or incomplete, may raise questions about the adequacy and reliability of the data, but those are matters that relate to the credibility of the opinion, not its admissibility. Without an evidentiary showing that Mr. Barker relied on data which would not be reasonably relied upon by experts in the field in forming the opinion Mr. Barker was asked to render, there is no basis for an appellate holding that, as a matter of law, the witness’s opinion testimony is inadmissible as mere speculation.
The second part of the majority’s rationale for reversal, although not specifically labeled as such, is that Mr. Barker’s testimony did not establish the correct measure of damages in that, although he presented a diligent mining plan — albeit it one with which my colleagues disagree — he did not testify as to the minimum amount of coal production that would be required to constitute diligent mining. Specifically, the court states:
Most importantly, although Mr. Barker testified that his plan would provide diligent mining, he did not testify that diligent mining required the amount of mining provided in his plan. He did testify that diligent mining required deep mining of the Kelly seam which G & W failed to do. However, he acknowledged that although his plan provided for mining 400,000 tons of coal a year, 250,000 or 800,000 could also be considered diligent. (Emphasis added.)
P. 771.
In the first place, the burden was upon the plaintiff to establish what a diligent mining plan would require. The expert did not say that diligence was determined by the amount of coal produced, but rather by the method of development over the life of the mine. Indeed, he stated that his idea of diligent mining did not depend upon the amount of coal that was produced. Specifically, he testified:
Let me explain what I think a diligent mining plan on this property or any property would be. That’s why I would not agree to any given tonnage for, whether it be 250,000 tons or 300,000.
In developing a plan, I used the reserves that were on the leases and planned to recover those or have an operation that would at least have an 18 — say a 15 to 20 year life. And I developed a plan that I thought was reasonable and under that plan, in a normal year, you *779would have about 500,000 tons. Depending on what interferences you might have with mining, whether you lost two or three months because of a strike, whether you had other losses because of weather or what have you, it would reduce that plan. Of course, that could be a diligent mining plan.
For me to just say that a 150 or 250 would be a diligent mining plan, I don’t think you can do that with this property. (Emphasis added.)
Mr. Barker also testified that a diligent mining plan required not only strip mining, but underground and auger mining as well. It is clear from his testimony that, in his opinion, the diligence of a mining effort is determined by the method used to develop the mining operations and not the minimum amount of coal produced.
G & W offered no testimony from its experts that diligence was determined by the amount of coal mined in any one year. In fact, one of G & W’s experts, Mr. O’Dell, testified that a plan of development is dependent upon the types of mining applicable to the land and the life of the mine. Such testimony is very similar to Mr. Barker’s testimony in this regard. It is true that G & W’s expert calculated that a lesser amount of coal would be produced under the mining plan developed by Mr. Barker. But he explained that his calculation of the amounts of coal produced by strip and auger mining were based upon the amount of coal actually mined by G & W. Such data is relevant to what G & W in fact did, but not to what it should have done under the Assumption of Obligations provision.
In the second place, Mr. Barker did not say, as the court claims, that “although his plan provided for mining 400,000 tons of coal a year, 250,000 or 300,000 could also be diligent.” What he did say, part of which is quoted above, is:
Let me explain what I think a diligent mining plan on this property or any property would be. That’s why I would not agree to any given tonnage for, whether it be 250,000 tons or 300....
For me to just say that 150 or 250 would be a diligent mining plan, I don’t think you could do that with this property.
As far as I’m concerned, with the assets that we had to work with, the leases, that is, I felt that a reasonable mining plan should mine, under normal conditions, say 450 to 500,000 tons a year.
To say that tonnage produced less than that was not a diligent plan, being specific about it, under the first and second year of my plan, I’ve accounted for the days in it and the reasons why the plan fell short. Now, I could not or wouldn’t feel comfortable in testifying that somebody else could develop a plan that would be maybe similar to mine but maybe not exactly like it.
It’s very difficult for me to sit here and say that a 200,000 ton production or say whatever, would not be a diligent mining plan or would be diligent. I hope I’m not confusing you. (Emphasis added.)
That testimony is a long way from a statement that “250,000 or 300,000 could also be diligent.”
Of course, no evidence was offered by anyone to the effect that mining production of 250,000 or 300,000 tons, or some lesser amount would be diligent mining. It is, at best, a strange contention that Mr. Barker’s opinion as to the requirements of a diligent mining plan was inadmissible speculation because it did not affirmatively reject a possible hypothetical opinion that a different mining plan resulting in smaller coal production would nevertheless be diligent, if indeed such an opinion were offered. It was the plaintiff’s burden to offer evidence to prove its case. It had no duty to offer evidence to impeach or contradict it.
In summary, once Mr. Barker was shown to be qualified under Fed.R.Evid. 702 to testify as an expert, he was entitled to give any opinion he had, whether or not it took into account all the relevant data a different expert, or this court, might like to have seen the witness evaluate, providing his opinion was based on data reasonably re*780lied upon by experts in the coal mining business. Moreover, such data need not be in evidence or admissible in evidence. Fed. R.Evid. 702.
Credibility determinations are for the finder of the fact and not for us. One of the functions of the fact finder in considering expert opinion testimony is to decide whether an expert’s opinion rests on facts or data adequate to support the opinion, and whether the facts or data are themselves persuasive. Those are matters that affect the credibility of the expert’s evidence, not its admissibility. See, e.g., Wrenn v. Gould, 808 F.2d 493, 499 (6th Cir.1987).
I would affirm the verdict and judgment below.