7. Graphs for Quantitative Data
1. Histogram
• A histogram is a special kind of bar graph that applies to quantitative data
(discrete or continuous).
The horizontal axis represents the range of data values. The bar height
represents the frequency of data values falling within the interval formed by
the width of the bar.
The bars are also pushed together with no spaces between them.
• A diagram consisting of rectangles whose area is proportional to the
frequency of a variable and whose width is equal to the class interval.
• Here the data values only take on integer values, but we still split the range of
values into intervals.
In this case, the intervals are [1,2), [2,3), [3,4), etc.
Notice that this graph is also close to being bell-shaped. A symmetric, bell-
shaped distribution is called a normal distribution.
13. • There are a couple of graphs that are appropriate for qualitative data that has no
natural ordering.
1. Bar graphs
• Bar Graphs are like histograms, but the horizontal axis has the name of each
category and
there are spaces between the bars.
• Usually, the bars are ordered with the categories in alphabetical order.
One variant of a bar graph is called a Pareto Chart.
These are bar graphs with the categories ordered by frequency, from largest to
smallest.
•Bars of a bar graph can be represented both vertically and horizontally.
•In bar graph, bars are used to represent the amount of data in each category; one
axis displays the categories of qualitative data and the other axis displays the
frequencies.
Graph for Qualitative (Nominal) Data
