Bar graphs are charts that compare two values: On one side they have a quantitative (number) amount and on the other side categories. The categories each have bars that are of heights to represent the amount. When the categories also represent a quantitative amount, like age ranges or time periods, the bar chart is called a histogram. Be very careful to read all information in the chart, including any keys or labels. Number amounts may be in hundreds or thousands.
Line graphs show change in quantitative amounts, usually over time. The line goes usually from left to right rising and lowering as the amount changes. Sometimes the chart may have multiple lines of different colors to compare. Use the key on the chart to know which color is which variable.
Pie charts are used to represent percentage parts of a whole amount. Be sure to read what the whole amount represented is. The wider the slice of pie, the larger the percent of the whole that category represents.
Scatter plots are used for recording multiple pieces of data that have two variables. Each data point is plotted on a graph. Often, a trend line is then drawn through the middle of the cluster of data points. The trend line can show a positive or negative relationship. If the line has a positive slope, the graph shows a positive relationship, meaning that as one factor increases, so does the other. If the line has a negative slope, the graph shows a negative relationship, meaning that as one factor increases, the other decreases. You can learn more about positive and negative slopes in the coordinate plane section.
Pictographs are similar to bar charts, but instead of using a bar, the use a set of symbols. Be sure to read the key to know how many units are represented by each symbol.
Dot Plots are graphs showing a list of values where, like a scatter plot, each piece of data is represented by one dot, but the x-axis (horizontal) represents the amount of each value and the y-axis (vertical) represens the number of times each of those values occurs in a list. The dot plot shown represents a list of values. Eight of those values are '7' because the 7 has eight dots above it. Two of the values are '8' because the 8 only has two dots above it.
Another way to represent a list of values is as a box plot or box and whisker plot. Each box represents a list of values. The top of the whisker, or line from the top of the box, represents the largest value in the list, and corresponds with the values on the y-axis. The top of the box represents the third or upper quartile (Q3), which means that one quarter of the values are above that line and three quarters are below it. The line in the middle of the box represents the median, or middle of the list of values. The bottom of the box represents the first or lower quartile (Q1), which means that one quarter of the values are less than that amount and three quarters are more. The bottom of the whisker below the box represents the lowest amount in the list of values. The box plot can be used to compare one list of values to others, as is shown by this example where the results of several experiments are compared.