Scatter Diagram with Strong Correlation.Scatter Diagram with Moderate Correlation.These are the most common in project management.ĭepending on the correlation, you can divide scatter diagrams into the following categories: I will discuss the two most popular based on correlation and slope of the trend. You can classify scatter diagrams in many ways. For example, you can use the fishbone diagram to find the two variables (cause and effect) and then use the scatter diagram to analyze their relationship. However, the fishbone or Ishikawa diagram can help you draw a scatter diagram. The scatter plot helps you analyze the correlation between the two variables. The fishbone diagram shows you the effect of a cause however, it does not show the relationship between these two. Note that these two diagrams are different. Many professionals believe that a scatter diagram is like a fishbone diagram because the latter includes two parameters: cause and effect. In that case, you can use any axis for any variable. There can also be two independent variables. It is not necessary to have a controlling parameter to draw a scatter diagram. The independent variable operates as the control parameter because it influences the behavior of the dependent variable. In most cases, the independent variable is plotted along the horizontal (x-axis), and the dependent variable is plotted on the vertical (y-axis). This reveals the correlation between the two. Once the drawing is complete, you notice that the number of accidents increases as the speed of vehicles increases. You select the two variables, motor speed and the number of accidents, and draw up the diagram. You are analyzing accident patterns on a highway. Scatter diagrams can show a relationship between elements of a process, environment, or activity on one axis and a quality defect on the other axis.” Example of Using a Scatter Diagram After determining how they are related, you can predict the behavior of the dependent variable based on the independent variable.Ī scatter plot is useful when one variable is measurable while the other is not.ĭefinition: According to the PMBOK Guide, a scatter diagram is “a graph that shows the relationship between two variables. The engineer performs a correlation analysis using the Pearson correlation to evaluate the strength and direction of the linear relationship between density and stiffness.The scatter diagram is considered the simplest way to study the correlation between these two variables. For more information, go to A comparison of the Pearson and Spearman correlation methods.įor example, an engineer at a manufacturer of particle board wants to determine whether the density of particle board is associated with the stiffness of the board. The Spearman correlation measures the monotonic relationship between two continuous or ordinal variables. If the relationship between the variables is not linear, you may be able to use the Spearman rank order correlation (also known as Spearman's rho). The Pearson correlation (also known as r), which is the most common method, measures the linear relationship between two continuous variables. You can choose between two methods of correlation: the Pearson product moment correlation and the Spearman rank order correlation. Use Correlation to measure the strength and direction of the association between two variables.
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