dissenting.
The jury accepted the testimony of defendant’s accident reconstruction expert that Greenwell was at fault. It rejected the testimony of eyewitnesses contrary to the expert’s reconstruction of the accident. On appeal, the plaintiffs claim correctly that the District Court erred in exercising its, gatekeeper function by admitting certain testimony and exhibits by the expert. The District Court’s error has led to a serious injustice.
The principal factual issue in the trial of this case was which vehicle caused the accident by switching lanes. The accident between the semi-tractor and the pickup occurred while both vehicles were traveling south on the Gene Snyder Expressway near Louisville during a heavy, summer rain storm. Before the collision, the pickup was in the left lane and the semi-tractor in the right lane. The semi-tractor was traveling without a trailer, ie., “bobtail-ing.” Right before the collision, Boat-wright in his semi-tractor attempted to leave the highway at an interchange by changing from the right lane to an exit lane on the right. As he decelerated to enter the exit lane, Boatwright, according to his own testimony, lost control of the semi-tractor when it began to “fishtail”— ie., the rear wheels of the semi-tractor skidded from side to side instead of following in the path of the front wheels. Boat-wright said in deposition testimony and at the trial that he attempted to regain control of his truck by braking and then releasing his brakes and “countersteering” in order to make the rear and the front of the truck move in the same direction. Boat-wright testified that he countersteered his truck to the left toward the pickup just before the collision occurred and then countersteered to the right after the impact. An eyewitness, Nicole Gray Besse, driving just behind the two, also testified that Boatwright was fishtailing immediately before the collision, veered to the left and struck Greenwell in the left lane. Two other eyewitnesses testified that the semi-tractor quickly veered from right to left just before the collision. None of these eyewitnesses were connected to the parties or had a motive to lie.
The defense paid Ken Razak to testify as an expert in accident reconstruction. Razak had an extensive academic background in mechanical engineering, had testified in previous cases well over 1000 times and was an impressive witness. Ra-zak testified that the physical evidence in the case (ie., the damage pattern to the *500two trucks and their final position after the collision on the right side of the road instead of the left) required the jury to conclude that the pickup caused the collision by veering right into the semi-tractor. The two trucks ended up on the right side of the highway with the pickup flipped over and resting on a guardrail. The left edge of the semi-tractor’s large, heavy front bumper tore into the pickup’s right fender just in front of its rear tire well and remained inserted in the fender until the front bumper bent 90 degrees forward to form an L with the top of the L pointing forward. From these two pieces of evidence — the bumper-fender damage and the fact that the trucks came to rest on the right side of the road — Razak testified that the accident had to have occurred because Greenwell veered to the right into Boat-wright’s lane of traffic. Razak was permitted to introduce and testify at length from six large well-constructed 3’ x 4’ drawings he had prepared showing the two trucks parallel to each other in the left and right lanes and then showing the pickup veering into the semi-tractor before they ended up on the right side of the expressway. The six large drawings from which Razak testified at length did not show the semi-tractor fishtailing with its rear wheels skidding from side to side, nor did it show the semi-tractor veering to the left, as Boatwright and the eyewitnesses testified.
During Razak’s direct examination, plaintiffs’ counsel objected to Razak’s analysis because it assumed that the semi-tractor was moving parallel to the pickup right before the accident. Counsel sought to have the District Court exercise its gatekeeper function by excluding the testimony of Razak when he stated as a scientific fact, and showed on his drawings, that the accident was necessarily caused when Greenwell veered into Boatwright’s lane. Plaintiffs’ counsel stated that Boatwright and the three eyewitnesses had testified that the semi-tractor was fishtailing or moving from side to side right before the accident and that Razak did not take this conceded fact into account. The District Court overruled the objection and stated simply that Razak was qualified to offer his opinion whatever it may be and could be cross-examined later by the plaintiffs.1
* :fc * * :¡: *
The question in this case is whether the District Court properly performed its gatekeeper function with respect to Razak’s expert testimony. He was allowed to testify at length, with the aid of his large drawings, the ultimate legal conclusion *501that Greenwell caused the accident by veering right into Boatwright. He was permitted so to conclude without taking into account the fishtailing movements of the semi-tractor or the fact that the accident could have happened just as the eyewitnesses described it.
Even before the Supreme Court’s landmark decision in Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), we required judges, to give a “hard look” and carefully assess the scientific conclusions and reasoning of experts because jurors are frequently overly impressed by conclusory opinions of scientific experts paid by a party. See Turpin v. Merrell Dow Pharm., Inc., 959 F.2d 1349, 1352 (6th Cir.1992) (excluding the scientific testimony of plaintiffs expert in a Bendectine case). Today, trial judges have an unequivocal duty to give careful scrutiny to the testimony of paid experts in order to avoid verdicts based on “junk science.” As the Supreme Court again stated this past term, Federal Rule of Evidence 702 “imposes a special obligation upon a trial judge to ‘ensure that any and all scientific testimony ... is not only relevant, but reliable,’ ” Kumho Tire Co. v. Carmichael, — U.S. —, —, 119 S.Ct. 1167, 1174, 143 L.Ed.2d 238 (1999), quoting Daubert, 509 U.S. at 589, 113 S.Ct. 2786. Under Daubert, trial judges must act as “gatekeepers” to undertake a “preliminary assessment of whether the reasoning or methodology underlying [expert] testimony is scientifically valid.” 509 U.S. at 592-93, 113 S.Ct. 2786. Although these principles designed to detect and exclude junk science are perhaps most frequently applied to plaintiffs’ paid experts, it is important that they should be applied equally to the experts of corporate defendants, as in this case. The rule is not one for plaintiffs experts only.
Trial judges must be on guard against all forms of junk science that may creep into the courtroom. In Kumho Tire, for example, the Supreme Court was wary of a generally reliable methodology perverted by an expert’s bogus analysis. The expert in Kumho Tire was retained to testify on the cause of a blown-out car tire. In his deposition, the expert reasoned that the blow-out was either caused by tire misuse or by a manufacturing or design defect. If the cause was misuse, the expert explained that the tire should reveal certain signs of stress. If a tire does not show at least two of these signs, the expert concluded that a design or manufacturing defect caused the blow-out. See — U.S. at —, 119 S.Ct. at 1172. The expert conducted a visual and tactile examination of the tires and found four signs of stress on the tire at issue. The expert testified that the signs were insignificant, however, and thus concluded that the blow-out was caused by a product defect and not by misuse. See id. at —, 119 S.Ct. at 1172-73. The Supreme Court held that the trial judge was correct in excluding the expert’s testimony because it was unreliable. See id. at -, 119 S.Ct. at 1179. The Court was careful to note that the practice of identifying tire misuse through visual and tactile inspection is generally reliable. See id. at —, 119 S.Ct. at 1178. The Court agreed with the trial court that the expert’s analysis was faulty because the expert concluded that a product defect caused the blow-out despite the identification of four indications of some misuse on the tire. The Court criticized the expert’s reasoning based on “fine distinctions” in identifying the signs of misuse and faulted the expert’s related standard of misuse because he rigidly required at least two signs of tire distress. See id. The Court reemphasized a court’s gatekeeper duties by closely analyzing the reasoning of the expert.
The case of Smelser v. Norfolk S. Ry. Co., 105 F.3d 299 (6th Cir.1997), holds that an expert opinion that relies on an untenable assumption rather than the evidence presented is unreliable. See id. at 305. Our Court held that the trial judge should have excluded the expert’s opinion on the *502cause of an accident victim’s injuries when the expert assumed that the victim had no pre-existing injuries. See id. The expert did not study the victim’s entire medical history and disregarded indications that he might have been injured similarly before. The expert also did not review the victim’s deposition or interview him about his symptoms or his version of how his body shifted during the accident. See id.
In this case, we have both a Smelser and a Kumho Tire problem. Like Smelser, Razak’s testimony, and his impressive drawings, were premised on an untenable assumption that Boatwright had full control over his semi-tractor and was traveling parallel with the pickup right before the accident. It disregarded the evidence. Both Boatwright and eyewitness Besse-Gray testified that the semi-tractor was fishtailing and out of control. Boatwright testified that he countersteered to the left just before the collision and to the right immediately afterward. By neglecting to take into account the course of the semi-tractor on the highway just before the accident, Razak foreclosed all possibility that the semi-tractor could have fishtailed into the pickup, hooked into the fender of the pickup and then pulled it to the right side of the road as Boatwright counters-teered in that direction. Razak testified that the vehicles would necessarily have ended up in the median on the left if Boatwright had veered to the left and struck Greenwell.
Razak’s disregard of evidence contrary to his theory leads to the deeper problem seen in Kumho Tire. Like the expert in Kumho Tire, Razak embraced a generally reliable science, i.e., accident reconstruction, but then corrupted it by restricting his theory of the accident by omitting the fishtailing evidence presented by plaintiffs’ witnesses and Boatwright. His legal conclusion that Greenwell was at fault was made to appear to the jurors as scientifically authoritative through his testimony and well-drawn exhibits. Razak limited his consideration of the collision essentially to two possibilities: (1) the pickup veered right into the semi-tractor or (2) the semi-tractor yawed left into the pickup without then changing direction to -the right after the collision. Nowhere do these two possibilities contemplate a collision caused by the semi-tractor veering left and then changing direction in an effort to regain control immediately after impact. This is a plausible proposition of fact even in the absence of the witness testimony. In the face of the uniform testimony of the eyewitnesses, it was incumbent on the expert to take it into account. By failing to consider it, Razak arrives at his single-minded conclusion that convinced the jury that the vehicles’ final position on the right side of the highway meant that Greenwell caused the accident by veering into Boatwright. Razak testified that the pickup must have caused the collision because it generated enough force to tip and roll over to the right after it had veered right into the semi-tractor. Just because such force would be sufficient, however, does not make it necessary. It is clearly possible that the eyewitnesses were right. The same force could have been generated by the semi-tractor veering left into the pickup and then right to regain control after the collision and pulling the pickup with its bumper inserted into the fender of the pickup. The semi-tractor’s force would have pointed the front of the pickup to the right. After being struck the pickup, attached to the semi-tractor bumper, would have traveled to the right as the semi counter-steered to the right. By ignoring this possibility — the one testified to by the eyewitnesses — -the expert was allowed to mislead the jury. The expert’s testimony and drawing showing his conclusion was allowed to come in on the theory that it could all be explored and corrected by cross-examination.
Judges after Tw"pin, Daubert, Kumho Tire and Smelser may no longer indulge in this assumption that an expert’s conclusions and reasoning can all be corrected by cross-examination as in the past. They *503must analyze the expert’s testimony carefully to see if the reasoning is “scientifically valid.” Daubert, 509 U.S. at 592-93, 113 S.Ct. 2786. Here the expert, paid to testify for defendant, was improperly allowed to exclude as a possibility the way the witnesses said the accident happened and promote another theory as “scientific” truth. He was allowed through testimony and drawings to give the imprimatur of scientific certainty to the idea that Green-well caused the accident because the trucks ended up on the right side of the road.
The District Court erred by admitting Razak’s testimony for the reasons above. Plaintiffs’ counsel attempted to alert the District Court of its gatekeeping duties by objecting to Razak’s testimony based on the assumption that Boatwright had full control of his vehicle right before the collision. The District Court should have assessed whether Razak’s single-minded theory was scientifically valid. Because the District Court failed to exercise properly its gatekeeping responsibilities, the judgment for the defendants should be reversed and remanded to the District Court for a new trial.
There is a growing tendency to apply the Daubert gatekeeper principles unequally against plaintiff but not corporate defendants. That has happened again in this case, I am sorry to say. In my view the rules excluding invalid scientific analysis should be applied to both sides. If that were done, Razak’s unscientific testimony — contrary to overwhelming evidence— that Greenwell ran the back end of his truck across into Boatwright’s front bumper would be excluded. The wreck clearly did not happen that way as the eyewitness testimony shows.
I am attaching an Addendum. It shows what the eyewitness testimony in this case was — contrary to the conclusory statements about it made on pages 496 and 497 of the majority opinion.
ADDENDUM
The majority claims that the testimony of the three eyewitnesses is in conflict. There is no conflict. All three testified that the semi-tractor fishtailed, lurched or spun to the left into the left lane and then went over the road to the right. So that the reader will have the testimony and can make up his or her mind, here is the relevant unimpeached testimony:
I.
The witness, Nicole Gray Besse, a high school Spanish teacher from Jasper, Indiana, was right behind the semi-tractor when the wreck happened and testified in relevant part as follows:
Q. How long in distance did you have an occasion to see the silver Ford pickup truck as you described it?
A At what point was I aware that it existed?
Q. Yes, ma’am.
A. Okay. Well, when I was coming around the curve and I was turning into — I was merging into the right-hand lane behind the tractor truck. It was, oh, perhaps between the two of us, but in the left-hand lane. And it was going, say, 55 miles an hour. And the truck in front of me was going faster than me. The tractor was going faster than me. I was going about 40 by then and the tractor is going faster than me, because I could see it accelerating even faster and made that jerky decision when it started jerking back and forth. The silver truck was like going to pass. It would have passed it easily if it had not been swinging back and forth to hit.
Q. What swinging back and forth?
A. The tractor was swinging back and forth with the fishtailing motion.
Q. Did the Ford pickup truck, the silver truck, did it ever leave the left lane before the impact with the tractor?
A. No, absolutely not.
*504Q. Where did the impact between the tractor and the Ford silver truck occur?
A. Where in position of me?
Q. Where in the position of the lanes you described?
A. I would say it was approximately in the middle of the merging zone, but in the left-hand lane.
Q. Don’t mean to confuse you and if you don’t understand the question, tell me. How did the tractor proceed from the exit area or attempting to exit to get to the left-hand lane?
A. It was the fishtailing motion. You could tell he was trying to get it under control, but he simply fishtailed. He couldn’t get it under control. After that first abrupt jerk to the right and back to the left, it kept fishtailing one, two, three, four.
Q. Could you ever determine the speed of the tractor?
A. It was going faster than me and I was going 40. Well, when it started fishtailing it might have been going a little slower simply because I had slowed down from my 40 miles an hour. I had slowed down as soon as I started seeing it fishtail. I thought, “Oh, I’m going to watch out for this guy.”
Q. Specifically did you ever see the Greemuell vehicle leave the left lane?
A. Absolutely not.
Q. Not until the impact?
A. Not until the impact and it was being dragged by the tractor over to the side because the tractor trailer was trying to get away from them.
(Tr., Vol.II, pp. 10-12) (emphasis added).
II.
The second eyewitness, Jill Raggard Schmidt, from Louisville, Kentucky, testified as follows:
Q. What do you recall about it?
A. Well, I was passing the ramp that would lead the people that were coming west on 64 up onto the Gene Snyder going south. I had just passed that ramp when I noticed a semi cab without the trailer immediately veer in front of me from the right-hand lane all the way to the far left lane. I thought that was odd because normally people stop at lanes in between changing lanes. It scared me because the weather was so bad, and I was afraid that I would lose control of my vehicle or possibly this person would hydroplane. And then he made it all the way to the far left lane and there was a big splash of water in front of him. I was still behind him in the right-hand lane. And the next thing I know he’s shooting off very quickly from the left-hand lane all the way across the right hand lane off the road into the grass. There was a ditch or a dip in the grass, so he went down and up and stopped. It was very fast. I was surprised that he didn’t turn over or, you know, seem to have any problem, but he came to a complete stop.
Q. I don’t want to—
A. He, the driver, of the semi cab.
Q. You’re talking bout the semi cab at this point?
A. Uh-huh.
Q. Continue.
A. I wanted to stop and make sure he was okay. And I began to slow down so my vision went off of him on my far right into my own lane, and then I noticed there was a vehicle or an object— at that point I didn’t know what it was— spinning in front of me still on the highway. And I thought for a brief second, “Well, maybe this is part of his cab. Maybe this is the trailer attached to his semi.” And then I remembered, no, he just had the semi cab. There was no trailer attached to it.
So I realized it was another vehicle and I knew that they wrecked and they were spinning around and they ended up hitting the guardrail. And at that point I slowed down and stopped where — at that point was an exit ramp to the right, so there was like a little V-shape of *505grass in the road before the guardrail where they had stopped. I pulled my ear off and got out and ran to the vehicle. There was two people inside: Mrs. Greenwell and her husband, and Mrs. Greenwell was alert. She was awake. She looked me and I don’t remember exactly what we said, but I do remember asking if she was okay, and she said she was. She said she was very worried about her husband And at that point other people had stopped, also.
Q. Did you ever see the Greenwell vehicle before you saw it spin in the road?
A. I did see an object. I was not focused on it. I knew there was something in the left-hand lane ahead of me. But I didn’t really pay that much attention to it because this semi cab took my attention once it merged and immediately started over. The next time I realized there was another car was when it was spinning in front of me.
(Tr., Vol.II, pp. 24-26.)
III.
Elizabeth Coulston from Louisville, Kentucky, testified as follows:
Q. Tell us what you observed that day. This was back—
A. I know I’m scared to death. I’m sorry. I was traveling on the Gene Snyder Freeway. It was raining. It started to rain very hard and I decided to slow down myself because in weather like that there’s always an accident somewhere that happens, so I thought I’d be safe. And I looked up ahead.
It was very difficult to see traffic to see other vehicles. And what I saw was the outline of a semi and I saw the semi go left and go around in a circle and it came back around and went off to the right and I saw a light pole, an interstate light pole snap like a toothpick. And I just kind of freaked out. “Oh, my gosh.” And I pulled over and went to see if everybody was all right.
Q. .The outline of the semi, were you able to determine where you first observed this outline?
A. I first — it was shortly before the ramp to the Interstate 64 to 64 east. I saw — I could see the back end.
Q. What lane of travel were you in?
A. I was in the left lane of traffic.
Q. What did you see the tractor or this outline, what did you see it do?
A. I saw it from the right-hand lane that the semi was in, I saw it go left across my lane. And it just circled around and then went off the right side of the road because I was scared it wouldn’t get straightened out before I got to it.
Q. Did you see the tractor, semi enter into the left lane?
A. Yes, I did.
Q. Did you ever see a silver pickup truck?
A. No, I did not. I never saw a vehicle in the left lane in front of me, and I’m sure it was because of the rain. I thought that the semi had just lost control and had an accident itself.
(Tr., Vol.II, pp. 35-36.)
All three eyewitnesses — the only eyewitnesses to testify — said basically the same thing. The semi-tractor lost control and fishtailed and lurched into the left hand lane from the right hand lane in which it was traveling. The first eyewitness who was nearest saw the semi-tractor strike the pickup truck. She was absolutely unequivocal in what she saw. Twice she told the questioner that she was “absolutely” certain that the semi-tractor left the right lane and struck the pickup truck in the left lane. The other two eyewitnesses were not as close and were hindered by the heavy rain in their vision. But they, too, saw the semi-tractor lurch from the right lane into the left lane and shortly thereafter realized that it had struck the pickup truck. It is obvious from this testimony— notwithstanding the court’s complete misinterpretation of the record — that the jury *506did not accept the consistent eyewitness testimony of the three witnesses. Rather, the jury accepted what in my opinion is the bogus, “junk science” testimony of the expert witness paid by the corporate defendant.
The outcome of this case represents a grave injustice to the family of the man killed by the negligent loss of control of the semi-tractor during a rain storm. I cannot sit idly by and watch such a grave injustice occur without registering my dissent.
. Plaintiffs objected as follows:
This analysis assumes that tractor was moving in a parallel direction on 1-265.... There has been no foundation laid that the tractor trailer was moving in a parallel direction on 1-265 at the time of this collision. In fact, all the evidence up this [sic] to date is that it was not moving at parallel fashion to 1-265, and we need to qualify that before this is introduced, because this fellow is suggesting that both vehicles were moving in a parallel fashion along 1-265, and that is not what is before this Court whatsoever, and that is not what’s before this jury.... What is before the jury at this point is this brown black tractor was out of control and was fishtailing and moving side to side and moving in a circular motion trying to exit 'to 1-64, not moving in a parallel fashion along 265.
Tr. pp. 23-24.
The trial judge did not analyze the expert's testimony but then ruled as follows:
THE COURT: I'm going to let him go ahead and testify, and you can cross-examine him on that point.
MR. WANTLAND: I understand, Your Hon- or. For the record and while we're here for the record, the idea of these trucks being parallel along the highway is a fact not in evidence, and we're not qualifying this witness.
THE COURT: Well, he’s qualified.
MR. WANTLAND: I'm saying I don't think that he’s qualified to answer the question.
THE COURT: He's qualified to testify as an expert. I'm going to let him come up with his theory. And if you think that there's some infirmity in it, then you can bring that out in cross-examination.
Tr. p. 25 (emphasis added).