How to Make Class Boundaries?

To create class boundaries, also known as real limits, you need to find the point midway between the upper class limit of one class and the lower class limit of the next higher class. This process effectively eliminates gaps between classes, creating a continuous data range.

Here's a step-by-step guide:

1. Identify Adjacent Classes: Locate two consecutive classes in your data. These classes should be directly next to each other, with no gaps in between. For example:

   Class	Values
   Class A	10-19
   Class B	20-29

2. Identify Upper and Lower Class Limits: Determine the upper class limit of the lower class (Class A in our example, which is 19) and the lower class limit of the upper class (Class B in our example, which is 20).

3. Calculate the Difference: Subtract the upper class limit of the lower class from the lower class limit of the upper class: 20 - 19 = 1.

4. Divide by Two: Divide the difference by 2: 1 / 2 = 0.5. This value represents the gap that needs to be filled to create continuity.

5. Adjust the Class Limits:

   • Lower Boundary: Subtract 0.5 from the lower limit of each class.
   • Upper Boundary: Add 0.5 to the upper limit of each class.

   Using our example:

   Class	Original Values	Class Boundaries
   Class A	10-19	9.5 - 19.5
   Class B	20-29	19.5 - 29.5

In Summary:

The formula to calculate class boundaries can be expressed as:

• Class Boundary = (Lower Limit of Upper Class + Upper Limit of Lower Class) / 2

Then:

• Lower Class Boundary = Lower Class Limit - (Class Boundary difference calculated above)
• Upper Class Boundary = Upper Class Limit + (Class Boundary difference calculated above)

Example:

Let's say you have the following classes:

• Class 1: 5 - 9
• Class 2: 10 - 14
• Class 3: 15 - 19

Following the steps:

1. Difference between Class 2 (10) and Class 1 (9) is 10-9 = 1.

2. Divide by two: 1/2 = 0.5

3. Class Boundaries:

   Class	Original Values	Class Boundaries
   Class 1	5-9	4.5 - 9.5
   Class 2	10-14	9.5 - 14.5
   Class 3	15-19	14.5 - 19.5

Class boundaries are important for creating accurate and meaningful histograms and other statistical visualizations. They ensure that each data point falls into exactly one class, avoiding ambiguity.