Hello SAP Experts,
What are Steps to create Multivariate chart?
Multi-Vari charts are easiest done with a computer, but not difficult to do by hand.
1) Plan the Multi-Vari Study.
Identify the y to be studied.
Determine how the y will be measured and validate the measuring system
Identify the potential sources of variation. For nested designs, the levels depend on passive data; for crossed designs, the levels are specifically selected for manipulation.
Create a balanced sampling plan or hierarchy of sources. Balance refers to equal numbers of samples within the upper levels in the hierarchy (i.e., two tools for each machine). A strict balance of exactly the same number of samples for each possible combination of factors, while desirable, is not an absolute requirement. However, there must be at least one data point for each possible combination.
Decide how to collect data in order to distinguish between the major sources of variation.
When doing a nested study, the order of the sampling plan should be maintained to preserve the hierarchy.
2) Take data in the order of production (not randomly).
Continue to collect data until 80% of the typical range of the response variable is observed (low to high). (This range may be
estimated from historical data.)
For fully crossed designs, a Multi-Vari study can be used to graphically look at interactions with factors that are not time
dependent (in which case, runs can be randomized as in a design of experiments).
3) Take a representative sample.
It is suggested that a minimum of three samples per lowest level subgroup be taken.
4) Plot the data.
The y axis will represent the scaled response variable.
Plot the positional component on a vertical line from low to high and plot the mean for each line (each piece). (Offsetting the bar at a slight angle from vertical can improve clarity.)
Repeat for each positional component on neighboring bars.
Connect the positional means of each bar to evaluate the cyclical component.
Plot the mean of all values for each cyclic group.
Connect cyclical means to evaluate the temporal component.
Compare components of variation for each component (largest change in y (Δy) for each component).
Many computer programs will not produce charts unless the designs are balanced or have at least one data point for each combination.
Each plotted point represents an average of the factor combination selected. When a different order of factors is selected, the data, while still the same, will be re-sorted. Remember, if the study is nested, the order of the hierarchy must be maintained from the top-down or bottom up of the sampling plan.
5) Analyze the results.
Ask Is there an area that shows the greatest source of variation? Are there cyclic or unexpected nonrandom patterns of variation? Are the nonrandom patterns restricted to a single sample or more? Are there areas of variation that can be eliminated (e.g., shift-to-shift variation)?