Are You Confident in Your Confidence?

Abstract

Chris and Fred discuss what it means to be ‘confident.’ Is it the way you carry yourself? Is it being able to rely or trust on something? Or is it the probability that some variable quantity will be within two limits? More importantly … what does this mean in the domain of reliability and quality?

Key Points

Join Chris and Fred as they discuss what it means to be ‘confident’ … particularly in the world of reliability. We have ‘confidence limits,’ ‘confidence levels,’ ‘confidence intervals’ … and of course … bosses who are ‘overly confident’ that the product reliability that they have spent no time focusing on won’t cause catastrophic problems later on. So what does ‘confidence’ mean to you?

Topics include:

Reliability and quality engineers often go straight to a ‘statistical’ interpretation of ‘confidence.’ For example, a reliability requirement may look something like …

… product X shall have a 90 % reliability at 2 years (warranty period) when used in accordance with use profile Y – WITH 99% CONFIDENCE

… and this is where statistics comes into play. Failure is a random process. So this requirement is all about having some sort of test or analysis approach where we BELIEVE that based on the data presented to us, there is a 99 % probability that our product meet its reliability requirements. So this is one sort of confidence.
The most useful form of confidence is one that is based on our PRODUCT, SYSTEM or SERVICE. For example, this could be based on FMEAs, HALT, or tailored approaches (such as where Netflix routinely trying to ‘break’ its systems in order to find weak points in the system) and then using this knowledge to focus ongoing reliability, software, and quality engineering efforts on those VITAL FEW elements of your system. This is the ‘ultimate’ form of confidence because it uses critical thinking in a way where we KNOW that every minute of effort is guaranteed to improve reliability. And there is always a finite amount of time we have … and that is the ‘limit’ to reliability improvement.
Another form of confidence is based on PASSING A TEST – but it is not the best. Why? Because the focus ceases to be the VITAL FEW and the TRIVIAL THOUSANDS … or what the standard document says is important. So we stop trying to make failures ‘happen’ in order to learn. Failures become the opposite of progress … so they are wished away. This form of confidence is all about ‘convincing’ yourself that you have done enough … not achieved enough.
Always focus on the decision. Are you confident that you are making the right decision? And making that decision EARLY usually awesome. Simple design characteristics that improve reliability are essentially free if they are part of your first design. They are free because we have the ultimate flexibility to make them simple. For example, if we work out that there is a thermally sensitive Printable Circuit Board (PCB) and that it should not be next to the exhaust manifold of a 20 cylinder diesel engine, our first blueprint can ensure that the PCB is a long way away from said exhaust manifold. And this is free. But … if we find out about this during our first production run … we might need to install insulation or some sort of additional cooling system that we have no room left for it in the engine bay. What would you rather do … have thousands of these free design characteristics incorporated early … or the couple of expensive remediations activities that we can afford to address the ‘big ticket’ items only … later?
Leaders who have relevant corporate knowledge are the key. Think of a military project to introduce a new tank into service. If the project leader is a tank officer who is very competent with lots of experience in driving tanks in the battlefield (not engineering) … then they have to rely on ‘bad’ types of confidence. This means passing tests or use standards or otherwise outsourcing critical thought to inanimate artefacts because the leader doesn’t have the skillset to do this him or herself.
So are you confident that you know what ‘confidence’ means?

Enjoy an episode of Speaking of Reliability. Where you can join friends as they discuss reliability topics. Join us as we discuss topics ranging from design for reliability techniques to field data analysis approaches.