Final answer:
The horizontal axis on a histogram represents the variable of interest, which is the range of data values organized into intervals. The heights of the bars indicate the frequency of observations within those intervals, showing the data's distribution.
Step-by-step explanation:
The horizontal axis on a histogram indicates the variable of interest. When constructing a histogram, one typically organizes data into intervals and counts how many observations fall into each interval. These intervals are plotted along the horizontal axis, which represents the range of data values. The vertical axis, by contrast, measures the frequency or relative frequency of observations within those intervals, often displayed as a count or percentage. For example, if the histogram is about the heights of a group of people, the horizontal axis would label the height intervals (e.g., 5'0"-5'2", 5'3"-5'5", and so on), and the vertical axis would show how many individuals are in each height range.
A histogram can reveal the distribution, center, and spread of data, helping to visualize the shape (such as normal, skewed, etc.) and the dispersion around the central tendency. It's a useful tool for understanding continuous data, where the different classes are represented by contiguous bars of varying height as per their frequency.