At 05:22 AM 11/18/2009, Steve Rooke wrote...
The point I should have made is that most quoted MTBF figures have a reasonable bearing on the lifetime of the item,
But your point would then be almost perfectly incorrect. MTBFs are not meant to, nor do they, predict product lifetimes. They are measures/predictions of product reliability.
"What does MTBF have to do with lifetime? Nothing at all!" - http://www.ece.cmu.edu/~ganger/ece546.spring02/readings/mtbf.description
"MTBF represents the statistical approximation of how long a number of units should operate before a failure can be expected. It is expressed in hours and does not represent how long the unit will last." - Learn (or review) the difference between MTBF and lifetime, Control Engineering, 9/24/2008; http://www.controleng.com/article/312365-Learn_or_review_the_difference_between_MTBF_and_lifetime.php
I don't grant Wikipedia strong authority, but it is useful, and has this to say: "MTBF is commonly confused with a component's useful life, even though the two concepts are not related in any way. For example a battery may have a useful life of four hours, and an MTBF of 100,000 hours. These figures indicate that in a population of 100,000 batteries, there will be approximately one battery failure every hour during a single battery's four-hour life span."
There's much more out there, if you make the effort.
I felt that an example based on humans was not really applicable to the real world of electronic items but that is my own opinion and I'm happy if you disagree with me.
MTBFs are not exclusive to electronics. Statistics, math and MTBFs are objective matters, so your opinion really doesn't make any difference.
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