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100% Inspection
Thanks for the information about the origins of effectiveness. The truth is a lot less simple! How difficult the inspection is decides how likely you are to find the problem. The example of "Is the fridge covered in paint?" is a good one. The likelihood of picking up an unpainted fridge when the primer is white is approx 100%. If the requirement is "Check the red paint coverage across the whole surface is a minimum of 0.25 mm thick and we're giving you a tape measure to check it" then the likelihood of finding a non compliance is somewhere near to 0%. Any other combination of checks and capability falls somewhere on or between these two markers.
The next point is that you cannnot add inspectors and bring down the probability. i.e 80% probability followed by 80% probability is not 64% probability of finding the problem. You have to take the opposite view. If the first inspector misses it what is the likelihood of the next inspector missing it 20% * 20% = 4%. Therefore the probability of two inspectors catching a fault becomes 96%. This assumes that the two inspections are not connected. i.e. the first inspection isn't cursory because "The next person will inspect it" or the 2nd inspection is cursory because "Well it's already been inspected."
I hope this has helped.
Thanks for the information about the origins of effectiveness. The truth is a lot less simple! How difficult the inspection is decides how likely you are to find the problem. The example of "Is the fridge covered in paint?" is a good one. The likelihood of picking up an unpainted fridge when the primer is white is approx 100%. If the requirement is "Check the red paint coverage across the whole surface is a minimum of 0.25 mm thick and we're giving you a tape measure to check it" then the likelihood of finding a non compliance is somewhere near to 0%. Any other combination of checks and capability falls somewhere on or between these two markers.
The next point is that you cannnot add inspectors and bring down the probability. i.e 80% probability followed by 80% probability is not 64% probability of finding the problem. You have to take the opposite view. If the first inspector misses it what is the likelihood of the next inspector missing it 20% * 20% = 4%. Therefore the probability of two inspectors catching a fault becomes 96%. This assumes that the two inspections are not connected. i.e. the first inspection isn't cursory because "The next person will inspect it" or the 2nd inspection is cursory because "Well it's already been inspected."
I hope this has helped.
