Page 282 - Lean six sigma demystified

260 Lean Six Sigma DemystifieD

Once you’ve learned the essence, it’s easy to add to that body of knowledge.
When you’ve learned the whole body of knowledge in one shot, it’s hard to
decide which portion to use and when.
? still struggling

You don’t need to know statistics to draw and use control charts. All you need
are the QI Macros and Excel.

Choosing a Control Chart

With the recently added I-MR-R chart, there are now 14 control charts in the
QI Macros. How do you know which one to use? When I’m working with data
in Excel, I follow a simple strategy for selecting the right chart based on the
format of the data itself. There are three formats I look for.

1. A single row/column
2. Two rows/columns with a numerator and a denominator
3. Two or more rows/columns containing multiple observations from each
sample

Single Row/Column

If you only have a single row/column of data, there are only three charts you
can use.

1. c chart (attribute or counted data). It’s always an integer (e.g., 1, 2, 3, 4, 5).
2. XmR chart (variable or measured data). It usually has decimal places
(e.g., 33.75).
3. XmR Trend chart. For variable data that increases (e.g., rising costs due to
inflation).
So which one should you choose? If you’re counting indivisible things like
defects, people, cars, or injuries, then choose the c chart. If you’re measuring
things like time, length, weight, or volume, choose the XmR chart. Look for
these patterns in the data and then select the chart.