Scatter diagrams are simple graphical methods used to study relationships between two variables. They can quickly determine if a relationship exists (positive or negative) and the strength of that relationship (correlation).
Scatter diagram procedures are:
• Decide how many points to plot. A minimum of 30 points is needed to make conclusions significant.
• Arrange the pairs of measurements in ascending value of x. Divide data into subgroups of x.
• Draw and label horizontal and vertical axes. Choose the proper scale to fit all points.
• If the diagram shows an upward trend, there is a positive correlation. A downtrend is negative, and a level trend implies no correlation between variables.
• It might be necessary to plot logarithmic scales or many y points to
a single x point to show data.