Create an interval plot for exam scores for different classes

Create an interval plot for exam scores for different classes

Problem Statement

The attachment shows a dataset of three groups representing exam scores of students from different classes.

How to perform analysis

Step 1: Open Sigma Magic
  1. Click on the Sigma Magic button on the Excel toolbar.
  2. Click on the New button to create a new project.
Step 2: Data Preparation
  1. Open the Supplier Data.xlsx attachment
  2. Select the data and convert it to table format by clicking Ctrl-T.


Step 3: Add the analysis template
  1. Click on the Tool Wizard to add the analysis template.
  2. Click on Graph and then Interval Plot.


Step 4: Specify analysis options
A new Interval Plot worksheet will be added to your workbook, and the following dialog box will be opened. Click on the Setup tab on the right. Accept the default values and specify the analysis options



Next, click on the Data tab and specify the data. Drag and drop the Table1 Sample size, Table1 Mean Score and Standard Deviation to the to the Analysis Variables and Table 1 Class to the Categorical Variables.



If you need to make changes to the charts, specify the optional settings in the Charts tab.

 Labels:

  • Add a title for the chart.
  • Label the X-axis and Y-axis appropriately.

Appearance:

  • Adjust colors, font sizes, or other visual elements as needed.
  • Enable/disable gridlines or background shading.
Finally, click the Verify tab to ensure all the inputs are okay and shown in a green checkmark.



Step5: Generate analysis results
Click on the OK button to generate analysis results. The following figure shows an example output screen.



How to interpret results

 The following conclusion can be drawn from this analysis.
  1. Class C scores the highest with significantly higher marks compared to Classes A and B.
  2. A lack of overlap between these confidence intervals implies that the difference is unlikely due to random change.
  3. Class A needs attention to improve scores, as it lags significantly behind the other classes.
Comparison of Means:
  • Class A has the lowest mean score (75).
  • Class B has a higher mean score (80) than Class A.
  • Class C has the highest mean score (85).

Variability in Scores:

  • Class B shows slightly higher variability (wider CI) due to a larger standard deviation (7) and smaller sample size (n = 25).
  • Class C has a narrower CI compared to Class B, reflecting less variability despite a smaller sample size.

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