Chapter 2: Stories Categorical Data Tell

A bar chart or pie chart is often used to display categorical data. These types of displays, however, are NOT appropriate for quantitative data. Quantitative data is often displayed using either a histogram, dot plot or a stem - and- leaf plot.

What Are Histograms?

In a histogram, the interval corresponding to the width of each bar is called a bin. A histogram displays the bin counts as the height of the bars (like a bar chart). Unlike a bar chart, however, the bars in a histogram touch on another. An empty space between bars represents a gap in data values. If a value falls on the border between two consecutive bars, it is placed in the bin on the right.

What Are Stem-&-Leaf Plots?

A stem-and-leaf plot is similar to a histogram, but it shows individual values rather than bars. It may be necessary to split stems if the range of data values is small.

A back-to-back stem-and-leaf plot can be useful when comparing two distributions.

The stems of the stem-and-leaf plot correspond to the bins of a histogram. You may only use one digit for the leaves. Round or truncate your values if necessary.

Stem-and-leaf plots are useful when working with sets of data that are small to moderate in size, and when you want to display individual values.

What Are Dotplots?

Dot Plots may also be used to display quantitative variables. Dot plots are useful when working with small sets of data.

Assignment:

A relative frequency histogram displays the proportion of cases in each bin instead of the count.

Histograms are usefull when working with large sets of data, and they can easily be constructed using a graphing calculator. A disadvantage of histograms is that they do NOT show individual values.

Be sure to choose an appropriate bin width when constructing a histogram. As a general rule of thumb, your histogram should contain about 10 bars.

How To Make A Histogram On Your Calculator

ASSIGNMENT: