Some Basic Statistics
Understanding the math is critical not only for the exam, but it is also important for your ability to function as a reliability professional.
Most of us did not enjoy our undergraduate statistics course. It was just another course to endure as part of being in an engineering or science track.
The basic concepts and approaches to working with data are fundamental for some many situations.
What does ‘mean’ or ‘average’ mean to you?
From our undergrad course, it’s the middle of the data or 50th%‘ile.
It where the mean, median and mode are the same…. wait, that is only for the normal distribution and then only when it’s not skewed or otherwise misshapen.
For the vast majority of the data, we deal with as reliability professionals, ‘mean’ is the 63rd%‘ile being part of the exponential family of distributions
The four functions
The other critical notion is the four functions that our various distributions take on as they describe life data.
Probability distribution function (PDF), Cumulative distribution function (CDF), Reliability function and Hazard function.
For your prep for the exam – you need to have these four functions and their relationship down. When is each useful and for what sort of questions?
That’s four equations for each of the life distributions. Common ones are the Exponential, Weibull and Lognormal distributions, yet there are many others.
The basic statistics section of the exam explores many of the basic statistics familiar to quality engineering, like data descriptions, plotting, variability, control charts, and Cpk.
Plus, the added statistics of life data distributions and related functions.
Yes, not everyone’s favorite topics, and considering the essential role it plays in our professional lives, and on the exam, you do need to do the homework.
In a recent discussion about CRE prep courses and how well they prepare students for the exam, we noted that the common pass rate for the exam is about 30%.
For those that ‘do the homework’ meaning that they work the examples and work out the problems, have about an 80% pass rate.
If being a course helps to motivate you to do the work, great. If you work sample problems on your own – great, too.
As I mentioned in a previous post – do the homework.
Role of reliability statistics (article)
The Exponential Distribution (article)