Lafferty has simply been told to assume that the lap belt unbuckled during the accident” and has “no independent opinion that the lap belt did, in fact, unlatch during the accident sequence.” NR 45:9. In response, Clark merely pointed to other testimony of Lafferty that contradicted these sworn statements by offering an opinion that the lap belt did come unbuckled. See NR 54, 68. Clark did not suggest that there was no contradiction in Lafferty’s testimony, or that Lafferty’s statements were limited to unbuckling “during the accident sequence.” As this argument was never raised below, it has been waived. Huntzinger v. Hastings Mut. Ins. Co., No. 96-4163, 1998 WL 205240, at *4 (7th Cir. April 28, 1998) (explaining that it is “‘axiomatic that an issue not first presented to the district court may not be raised before the appellate court as a ground for reversal’”), quoting Christmas v. Sanders, 759 F.2d 1284, 1291 (7th Cir. 1985).
Because Clark offers no plausible basis for upsetting the district court determina- tion that Lafferty’s testimony was not sufficiently “helpful to the trier of fact” to be admissible (NR 87:16; see Fed. R. Evid. 702), there is no need to consider whether the district court’s second rationale would survive review for abuse of discretion. But, in any event, the second rationale is unassailable, as we next explain.
The district court did not abuse its discretion in concluding that Lafferty’s opinion concerning the lap belt should be stricken because it was not based on a reliable methodology under Daubert. Lafferty’s principal theory was that the seat belt must have unbuckled because it permitted at least four inches of movement. In his report, Lafferty opined that “if Mr. Clark’s lap belt had functioned properly, he would have been restrained from impacting the roof of the Honda and he would have had no serious injury in this accident.” NR 87:9. He explained: