5.8 Basic Lean Tools: Scatter Diagram

The scatter diagram is a visual method to see a relationship between two items. Say you want to buy a used car: you know that many variables impact the cost of the vehicle. These could include brand, model, condition, and age, to name a few. So, you intuitively know that age has an impact on price.

While the example may not be a realistic look at used car prices, it should give you an idea of the relationship between the age and price of used cars you are considering. It should be noted that an exemplary scatter diagram would hold the other variables, or factors, constant. If this were an actual data collection, all the prices would be for the same make and model car. Then, you would see the relationship using the scatter diagram.

There are two things you should consider when using a scatter diagram.

• The numerical pair dataset. Consider the age and price of used cars; the example is a deliberately simple pair for which most people will instantly recognize the relationship.

• Relationships between less obvious pairs. For example, the pair of data items might be new employee orientation training days and mislabeled pallet barcodes. There may or may not be a relationship, but by plotting the numbers on the scatter diagram, a visible result will help you determine if there is a relationship.

A scatter diagram is the first of two tools to examine the relationship between items. In a later chapter, we will look at how to make a scatter diagram and apply some statistics to determine the strength of the connection using regression. But for our immediate purposes, the scatter diagram can often demonstrate enough of a relationship to take corrective actions by helping to identify the root cause.