Statistical Graphs

StudyWeb Award
January 2001

Data recorded in experiments or surveys is displayed by a statistical graph. We will discuss eleven types of statistical graphs. Choosing which graph is determined by the type and breadth of the data, the audience it is directed to, and the questions being asked.

Each type of graph has its advantages and disadvantages. Consult the table below when choosing a graph. Each entry in the table has a link to an example of that graph. Just click on the underlined name of the graph.

NCES Create a Graph
EIA Guidelines for Statistical Graphs

Pictograph A pictograph uses an icon to represent a quantity of data values in order to decrease the size of the graph. A key must be used to explain the icon.	Advantages Easy to read Visually appealing Handles large data sets easily using keyed icons	Disadvantages Hard to quantify partial icons Icons must be of consistent size Best for only 2-6 categories Very simplistic
Line plot A line plot can be used as an initial record of discrete data values. The range determines a number line which is then plotted with X's for each data value.	Advantages Quick analysis of data Shows range, minimum & maximum, gaps & clusters, and outliers easily Exact values retained	Disadvantages Not as visually appealing Best for under 50 data values Needs small range of data
Pie chart A pie chart displays data as a percentage of the whole. Each pie section should have a label and percentage. A total data number should be included.	Advantages Visually appealing Shows percent of total for each category	Disadvantages No exact numerical data Hard to compare 2 data sets "Other" category can be a problem Total unknown unless specified Best for 3 to 7 categories Use only with discrete data
Map chart A map chart displays data by shading sections of a map, and must include a key. A total data number should be included.	Advantages Good visual appeal Overall trends show well	Disadvantages Needs limited categories No exact numerical values Color key can skew visual interpretation
Histogram A histogram displays continuous data in ordered columns. Categories are of continuous measure such as time, inches, temperature, etc. Histogram Explorer	Advantages Visually strong Can compare to normal curve Usually vertical axis is a frequency count of items falling into each category	Disadvantages Cannot read exact values because data is grouped into categories More difficult to compare two data sets Use only with continuous data
Bar graph A bar graph displays discrete data in separate columns. A double bar graph can be used to compare two data sets. Categories are considered unordered and can be rearranged alphabetically, by size, etc.	Advantages Visually strong Can easily compare two or three data sets	Disadvantages Graph categories can be reordered to emphasize certain effects Use only with discrete data
Line graph A line graph plots continuous data as points and then joins them with a line. Multiple data sets can be graphed together, but a key must be used.	Advantages Can compare multiple continuous data sets easily Interim data can be inferred from graph line	Disadvantages Use only with continuous data
Frequency Polygon A frequency polygon can be made from a line graph by shading in the area beneath the graph. It can be made from a histogram by joining midpoints of each column.	Advantages Visually appealing	Disadvantages Anchors at both ends may imply zero as data points Use only with continuous data
Scatterplot A scatterplot displays the relationship between two factors of the experiment. A trend line is used to determine positive, negative, or no correlation.	Advantages Shows a trend in the data relationship Retains exact data values and sample size Shows minimum/maximum and outliers	Disadvantages Hard to visualize results in large data sets Flat trend line gives inconclusive results Data on both axes should be continuous
Stem and Leaf Plot Stem and leaf plots record data values in rows, and can easily be made into a histogram. Large data sets can be accomodated by splitting stems.	Advantages Concise representation of data Shows range, minimum & maximum, gaps & clusters, and outliers easily Can handle extremely large data sets	Disadvantages Not visually appealing Does not easily indicate measures of centrality for large data sets
Box plot A boxplot is a concise graph showing the five point summary. Multiple boxplots can be drawn side by side to compare more than one data set. More about boxplots here.	Advantages Shows 5-point summary and outliers Easily compares two or more data sets Handles extremely large data sets easily	Disadvantages Not as visually appealing as other graphs Exact values not retained