Quote Originally Posted by dsiegel5151 View Post
This is why I quit reading DxO [...] I don't see how these measurements give one sensor a score of a 95 and the other a score of an 81.
It's pretty simple. You measure three areas of performance (DxO's portrait, landscape, and sports scores) and then average them together. The D800 sensor did better in all three, so it had a higher combined score.

Quote Originally Posted by dsiegel5151 View Post
Here's another example: [...] Notice that the Pentax K5 has scored an 82 overall; however, it is inferior to the 5d Mark III in ever category except Dynamic Range at low Iso settings. Thus, am I to infer that Dynamic Range at low Iso settings is the only measurement that matters when rating a sensor?
No. Say Johnny gets 65% in Chemistry, 65% in English, and 100% in Math. While Sally gets 70% in all three. Sally beat Johnny in two out of three subjects, but Johnny's GPA is still higher. Are you to infer that Math is the only subject that matters when calculating someone's GPA?

Any time you try to reduce something down to a single number, it will *not* reflect the full reality and complexity of the situation.

Summarizing something as complicated and nuanced as sensor performance into a single number is impossible. But a lot of people *want* a single number, because they don't have the time or inclination to learn all that stuff. So DxO provides the solution for everyone.

At one end of the spectrum (technically-minded folks), it provides the full charts and data so you can go in and see how it really does for yourself. Make up your own metrics that reflect what you do with the camera, and use their data for it.

Towards the other end of the spectrum, DxO has chosen three particular measurements, that while they may not match your shooting exactly, they do reflect the taste and perception of many photographers. You merely choose how important each of these three are to you and weight them yourself (for one, low light may be twice as important as dynamic range and color depth; for another photographer, the reverse).

Then at the very end of the spectrum you have folks for whom even three numbers is too much. They only have time or inclination to compare based on a single number. DxO doesn't know how important the three factors are for every person, so they just weight them equally. I think that's a good choice, even though it doesn't match the weighting that I would use for myself, personally.