I've not insulted you; I've simply pointed out you misunderstand statistics. Your last post firmly cements this position. Nothing in that WD statement contradicts me, nor does it imply that MTBF "does not mean anything". If you'll climb down off your high horse for a moment and listen, you'll understand why. Let me start the explanation a bit further back.I admire how confident you are in your incorrectness while feeling the need to continually try to insult me and accuse me of not knowing what I am talking about....Western Digital has put in writing that MTBF does not mean anything
You have a mechanical item -- hard drive, automobile, anything. You want to know if it will break down over a specified period of time. Assuming the period is shorter than the "wear-out" period, then you're asking about random faults, which by definition cannot be predicted, no more than you can predict whether the next flip of a shuffled card deck will reveal an ace. All you can predict is probabilities. Not certainties.
With me so far? This is what WD (and all manufacturers of all fault-rated components and equipment) mean when they say their data "does not predict an individual units reliability and does not constitute a warranty". A one-million hour MTBF is not a statement that your drive will run one million hours. It's a statement of probabilities only. That doesn't make it "meaningless". Far from it.
How do you predict experimentally the probability of an ace of spades appearing in a single flip of a deck of cards? (Let's assume the deck composition is unknown, so you can't simply calculate that mathematically). You run experiments, that's how. You flip a card, reshuffle, and flip again. Each of these events is a sample. (Note-- the card flip you're attempting to predict is NOT a sample, nor is the hard drive you own that you wish to know its failure chance. This is the explanation for my earlier statement that you were misinterpreting sampling).
With a large sample size, you can calculate probabilities for the random single-event case you're interested in. The more samples, the better the sample space reflects the entire statistical universe of possible events. But this sample space still applies to single events, but on a probabilistic, rather than a deterministic basis. In the case of MTBFs, even though they're not expressed as percentages, they're still simply probabilities, not warranties of performance. And they are far from meaningless, which is why every manufacturer of critical components goes to such great lengths to calculate those numbers.