Question

For data that are grouped in classes based on more than a single value, lower-class limits (or cut points) are used on the horizontal axis of a histogram for depicting the classes. Classmarks (or midpoints) can also be used, in which case each bar is centered over the mark (or midpoint) of the class it represents. Explain the advantages and disadvantages of each method.

Short answer

In the case of midpoints, the histogram bar is centred over the class's midpoint mark.

Step-by-step solution

Concept introduction

The average of the upper and lower class limits is called a midwaypoint. The lowest value in a bin is the lower class limit; the greatest values that can be in the bin are the upper class limits.

Explanation

Data that is based on more than one value is grouped, and classes are created. On the horizontal axis of a histogram, lower class boundaries or cutpoints are used to show the classes. Also utilised are class marks or midpoints. In the case of midpoints, the histogram bar is centred over the class's midpoint mark.

In terms of utility, both methods are equal.

When the class width is odd, the class's midpoint will be an integer number, hence it's best to utilise the midpoint mark. If the class width is even, the midpoint will be a decimal value. As a result, cutpoints are a superior option in this case.