What do I use
Engineering, manufacturing and quality
Process control, quality assurance, reliability, operations research.
Your question, and what answers it
X-bar and R for subgroups, individuals when measurements come one at a time. Do this first.
In ZStat: open your study, go to Analysis, and choose control chart.
Cp, Cpk and expected defects per million - and only after stability, because an index describes a distribution an unstable process does not have.
In ZStat: open your study, go to Analysis, and choose process capability.
With a post-hoc test rather than repeated pairwise comparisons.
In ZStat: open your study, go to Analysis, and choose one way anova.
Which is where the interesting answer usually is.
In ZStat: open your study, go to Analysis, and choose factorial anova.
Including the units that had not failed when testing stopped, which is the whole point of survival methods.
In ZStat: open your study, go to Analysis, and choose kaplan meier.
With a margin agreed before the trial, not after.
In ZStat: open your study, go to Analysis, and choose non inferiority.
What goes wrong in engineering, manufacturing and quality
- Drawing control limits from the specification. That chart cannot show the process drifting inside tolerance, which is the reason to draw it.
- Capability indices on an unstable process.
- Charting data that has been sorted. The chart will look beautifully stable and mean nothing, and no statistic can detect it.