![]() ![]() A numerical measure of linear relationship between two variables is given by Karl Pearson’s coefficient of. A scatter diagram visually presents the nature of association without giving any specific numerical value. The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. However, is there a link between increasing childhood obesity and increasing disposal incomes for households? Both these variables have risen over the long-term, but they are probably not directly related. to measure correlation are scatter diagrams, Karl Pearson’s coefficient of correlation and Spearman’s rank correlation. It is logical to believe that there is a causal link between the daily temperature and sales by ice-cream vans. This scatter plot, from Miller, Moore, Richards. A screening survey to assess local public health performance. (The data is plotted on the graph as 'Cartesian (x,y) Coordinates') Example: The local ice cream shop keeps track of how much ice cream they sell versus the noon temperature on that day. In this example, each dot shows one person's weight versus their height. Its important to note that scatter plots show correlation between two variables. A Scatter (XY) Plot has points that show the relationship between two sets of data. The big danger with correlation is of believing there is really a causal link between two variables when, in fact, they are not related. Scatter plots can be effective in measuring the strength of relationships uncovered with a fishbone diagram. If the data suggests strong correlation, then the relationship might be used to make marketing predictions. Weak correlation means that the data points are spread quite wide and far away from the line of best fit. Strong correlation means that there is little room between the data points and the line. The line of best fit indicates the strength of the correlation. No correlation: There is no discernible relationship between the independent and dependent variable Negative correlation: A negative relationship exists where as the independent variable increases in value, the dependent variable falls in value Positive correlation: A positive relationship exists where as the independent variable increases in value, so does the dependent variable There are three kinds of possible correlation: This can be drawn by hand or using an Excel spreadsheet or specialist marketing software. Example scatter plots A screening survey to assess local public health performance This scatter plot, from Miller, Moore, Richards, and McKaig, shows the correlation between survey responses and screening queries for an assessment of local public health performance. The answer is a "line of best fit" (the regression line) which attempts to plot the mathematical relationship between the variables based on the data points. How can a marketing manager make sense and use of all the data points once they have been plotted on the scatter diagram? Dependent variable (the variable being influenced by the independent variable) on the y-axis. ![]() Independent variable (the factor that causes the other variable to change) on the x-axis Examples of Scatter Diagrams Limitations of a Scatter Diagram Scatter Diagrams for The PMP Exam Scattering Wisdom Frequently Asked Questions (FAQs) View All If you’re a project manager, you’ll know that making decisions is a part and parcel of your job, daily. ![]()
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