This may seem like splitting hairs to some people, but I both somewhat agree and disagree with the above statement:
First of all there are inaccurate scans from drives that show impossible values, such as NEC drives showing more than 1664 PIE per 8 ECC blocks, or more than 1664/208 PIF per 8/1 ECC block. There is no way such a result can be considered accurate because it is theoretically impossible!
Second of all I think there is a closely related concept which I will call a "useful scan". Also the "precision" (using muchin's linked article about accuracy and precision) or repeatability of scans differ between drives.
I define a "useful scan" as a scan that helps to discriminate between media that can easily be read in a number of drives and media that cannot easily be read in a number of drives. If the scans from a drive cannot be used for that purpose, then I deem it to be "not useful". Usefulness doesn't necessarily depend on "accurate" PIE, PIF, Jitter or other values, but it has to be somewhat precise or repeatable.
An example of a "not useful" scan would be e.g. scanning CDs (not DVDs) on a LiteOn SHW-1635S drive. Such scans can show extremely low C1 errors and a limited number of C2 errors, and the disc is still unreadable in almost all drives!
An example of a useful scan that is precise but not accurate is a Read Transfer scan, provided that it is performed on a drive that is not defective, too picky, or which reads everything. Read Transfer scans from my NEC 3500 have proven useful: It is repeatable (i.e. precise) and it is a good predictor for whether the disc can be read back on other drives. A Read Transfer test on a LiteOn drive might not be as useful, because LiteOn drives will often read discs without any drop in speed, where the same discs cannot be read in many other drives - hence it isn't as useful.
Scans at 5x and 8x on my NEC 4551 drive (not necessarily all drives of this family) are not always useful, because they are not precise, and the drive or scanning software will sometimes randomly report extreme peaks of PIE and PIF errors. Scanning on the same drive at 12x seems more precise in practice with the limited number of tests I have done, and scans at 1x are even better (but very slow).
The point on which I agree with rdgrimes and many other people is, that the PIE and PIF errors are not on the disc per se, but are generated during the reading process. So it is wrong to think of scanning as a true measurement of a precise and accurate value on the disc itself.