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## About this lesson

Graphical analysis techniques are particularly good for illustrating significance, similarities or differences, and correlation between parameters within a data set.

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## Quick reference

### Visual Analysis

Graphical analysis techniques are particularly good for illustrating significance, similarities or differences, and correlation between parameters within a data set.

### When to use

The graphical analysis techniques work very well when there is either a special cause problem or a singular root cause for the problem. In those cases, it is often faster to use the graphical visual analysis than a statistical analysis. Also, it is much easier to explain the problem to stakeholders and team members using visual analysis than with statistical analysis.

### Instructions

Different types of graphs can be used for visual analysis depending upon the question or hypothesis that is being asked. Using a graphical analysis technique provides a visualization of the data that can quickly lead to conclusions about the problem.

When looking for significance of a parameter or significance within a parameter, use the vertical bar chart or horizontal bar chart. The Pareto chart, which is a special case of the vertical bar chart, is particularly useful. The pie chart can also be used in some cases, but it is normally used in families of pie charts, so either the charts will show that an item is significant in some instances (pies) and not in others, or that it is significant in many different instances (pies). Either of those may be very important information to prove or disprove a hypothesis.

Graphical techniques are also useful for visualizing similarities and differences. This can either be similarities between data sets using box plots or similarities and differences over time using run charts. In the first case, the box plots reveal which data sets are different, providing insight into underlying causes for the problem. In the second case, the run chart shows when a difference first occurred, providing insight into the occurrence of a special cause problem that must be addressed in order to get a stable process.

Graphical techniques can also show a relationship between two parameters. A scatter diagram shows a positive correlation if the data has a clear upward trend and a negative correlation if the data has a clear downward trend. If there is no trend in the data, the two factors are independent of each other. While the scatter diagram shows a relationship, it does not indicate which factor is dependent and which is independent. In fact, both factors could be dependent upon a third factor. Therefore, correlation does not mean causation, only that there is relationship.

### Hints & tips

- Once the data is captured in a database or table, it is easy to create charts and graphs in both Excel and Minitab. It only takes a few mouse clicks, so visualize the data first before jumping into statistical analysis.
- Graphical or visual analysis is particularly well suited to single factor problems and special cause problems. That is why some of the basic problem solving methodologies rely solely on visual analysis.

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