What Is Chunky Data?

What happens when the measurement increment gets too large?

Many times measurements are made using measurement increments which are too large for the job. Fortunately this problem is easily detected by ordinary, production-line process behavior charts. No special studies are necessary; no standard parts or batches are needed. You simply need to recognize the telltale signs. It is the purpose of this column to explain these signs of chunky data, to outline the nature of the problem that causes chunky data, and to suggest what can be done about it when it occurs.

Most problems with process behavior charts are fail-safe. That is, the charts will err in the direction of hiding a signal rather than causing a false alarm. Because of this feature, when you get a signal, you can trust the chart to be guiding you in the right direction. Chunky data is the only exception to this fail-safe feature of the process behavior chart.

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Comments

Thanks for the Amplification

I've been using this rheostat data example ever since the first time I read Understanding Statistical Process Control, and went to the Advanced Topics seminar. I've found chunky data in almost every industry with which I've worked--including banking, where they were measuring transaction times to the nearest minute (and needed to measure to the nearest second). This concept was a key factor in helping diagnose some helicopter engine test data for the Marines, and developing a new test procedure that ended up saving thousands of hours of rework and thousands of gallons of oil every year. This new amplifying information is a great dive into the concepts!

False Precision

Thank you for your insight.

Throughout my the dimensional metrology career I tend to make the users of the equipment as well as the users of the data aware of the negative effects of false precision as well. Rounding, Turncation or Ignoring decimals could bring problems later on.