3 ms·

> I also like to put my faith in a human (or multiple humans) then going over it again "just in case"... in this case it would be someone following behind with

by jen20 8y ago

> I also like to put my faith in a human (or multiple humans) then going over it again "just in case"... in this case it would be someone following behind with another torque wrench to make sure the first guy hadn't missed something or was maybe using a defective wrench. A second pass with a torque wrench is probably not such a bad idea, but multiple _checks_ by humans is not necessarily beneficial. A few years ago I worked for a company making small-batch pharmaceuticals (almost exclusively with ingredients drawn and mixed by hand, since the batches were so small), and the consensus (backed by research) there was that adding a second human check made quality worse rather than better - the second checker assumes that the first did the job correctly, and the person doing the work assumes that mistakes will be caught further down the line.

keithpeter 8y ago
Very interesting, thanks for posting. No sampling at all? No samples retained for analysis in the event of a problem later?
- jen20 8y ago
  Depending on the criticality of the actual substances for the given use (both of which were always known), assay of samples may have been required as an in-process control rather than an out-of-band one, too. By "small-batch" I often mean batches of one-offs, reducing the effectiveness of sampling for quality control!
  - keithpeter 8y ago
    "By "small-batch" I often mean batches of one-offs, reducing the effectiveness of sampling for quality control!" But increasing the importance of a sample retained for later analysis I imagine.
sitkack 8y ago
The solution is for the checkers to be blind, in that they should have no knowledge of ordering or checks. Everything needs to be independent. It isn't that the second check made quality worse, it is that knowledge that the second check is run made the first or second check less rigorous. 1) inject faults to test the testers 2) test diversity, automated and manual 3) test order inversion The often used alternative is to "be careful" which is not rigorous.
- jen20 8y ago
  Indeed, that is the root cause, rather than a second check itself.

by jen20 8y ago

keithpeter 8y ago

Very interesting, thanks for posting. No sampling at all? No samples retained for analysis in the event of a problem later?

jen20 8y ago
Depending on the criticality of the actual substances for the given use (both of which were always known), assay of samples may have been required as an in-process control rather than an out-of-band one, too. By "small-batch" I often mean batches of one-offs, reducing the effectiveness of sampling for quality control!
- keithpeter 8y ago
  "By "small-batch" I often mean batches of one-offs, reducing the effectiveness of sampling for quality control!" But increasing the importance of a sample retained for later analysis I imagine.

sitkack 8y ago

The solution is for the checkers to be blind, in that they should have no knowledge of ordering or checks. Everything needs to be independent. It isn't that the second check made quality worse, it is that knowledge that the second check is run made the first or second check less rigorous. 1) inject faults to test the testers 2) test diversity, automated and manual 3) test order inversion The often used alternative is to "be careful" which is not rigorous.

jen20 8y ago
Indeed, that is the root cause, rather than a second check itself.