This tool can be implemented as an effective way to display what happens to one variable when another variable is changed. The diagram is used to test a theory that the two variables are related. The type of relationship that exists is indicated by the slope of the diagram. A scatter diagram (also called scatter plot) is composed of a horizontal axis containing the measured values of one variable and a vertical axis representing the measurements of the other variable.
Want to know more about a Scatter diagram?? Here is a link.
By now you must be wondering when and how to use a scatter diagram….
When do I use a scatter diagram?
Use a scatter diagram to design a control system to ensure that gains from quality improvement efforts are maintained.
How do I use a scatter diagram?
- Collect data. Gather 50 to 100 paired samples of data that show a possible relationship.
- Draw the diagram. Draw roughly equal horizontal and vertical axes of the diagram, creating a square plotting area. Label the axes in convenient multiples (1, 2, 5, etc.) increasing on the horizontal axes from left to right and on the vertical axis from bottom to top. Label both axes.
- Plot the paired data. Plot the data on the chart, using concentric circles to indicate repeated data points.
- Title and label the diagram.
- Interpret the data. Scatter diagrams will generally show one of six possible correlations between the variables:
- Strong Positive Correlation -The value of Y clearly increases as the value of X increases.
- Strong Negative Correlation -The value of Y clearly decreases as the value of X increases.
- Weak Positive Correlation -The value of Y increases slightly as the value of X increases.
- Weak Negative Correlation -The value of Y decreases slightly as the value of X increases.
- Complex Correlation -The value of Y seems to be related to the value of X, but the relationship is not easily determined.
- No Correlation -There is no demonstrated connection between the two variables.
Remember, when making a scatter plot, DO NOT connect the dots!
Here is another way to help you understand scatter diagram better. Simply follow this link!
Now that you know all about scatter diagrams let’s try an example…
Notice: Certain values may have more than one result,
such as (7,90) and (7,85) and (7,100).
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The data displayed on the graph resembles a line rising from left to right. Since the slope of the line is positive, there is a positive correlation between the two sets of data. This means that according to this set of data, the longer I study, the better grade I will get on my Regents examination.
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Note: Just because this set of data showed a positive correlation, it does not mean that the relationship is positive for all sets of data concerning study time and Regents scores. There may be sets of data that show that there is NOT a positive correlation between hours studying and better Regents scores. It all depends on the data being examined.
If the slope of the line fell from left to right, a negative correlation would exist since the slope of the line would have been negative. Under a negative correlation, the longer I study, the worse grade I would get on my Regents examination.
If the plot on the graph is scattered in such a way that it does not approximate a line (it does not appear to rise or fall), there is no correlation between the sets of data. No correlation means that the data just doesn't show if studying longer has any effect on Regents examination scores.
Great! You have just completed an example of Scatter Diagram. Here is another example you can use for practice. Enjoy learning Click Here
Evaluation:
Candy Creations has been receiving a number of complaints about one of their popular candy Tropical Paradise. A survey was conducted and identified that the brix level was inaccurate, thus causing the candy to crumble. Using the data provided below, draw a scatter diagram to show an appropriate relationship between the two variables. Describe the type of correlation that you observe in order to assist Mr. George, the production manager in assigning the patterns of causes for the complaints. Good luck
| BRIX LEVEL | CRUMBLED CANDY |
| 2 | 10 |
| 3 | 18 |
| 4 | 20 |
| 12 | 29 |
| 20 | 31 |
| 35 | 35 |
| 39 | 39 |
| 56 | 40 |
| 61 | 42 |
| 72 | 59 |
| 79 | 61 |
| 84 | 64 |
| 98 | 68 |
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