A scatter plot is a type of graph that relates two paired sets of data. It is useful for trying to find the correlation between the two data sets. Here’s how to make a scatter plot:
- Draw a grid. First, draw a horizontal line (X Axis). Then, draw a vertical line (Y Axis) intersecting the center of the horizontal line. This is best done on graph paper because you will be able to precisely plot each point of data rather than guessing its approximate location. If all of your data points are positive numbers rather than negative, you do not need the whole grid. Instead, draw an L shape facing right. The bottom edge of the L is the X axis, and the vertical edge is the Y axis.
- Label each axis. The scale you use depends on the data you need to plot. For example, your scale may go from 1 to 10, with labels at every whole number. It may go from 1 to 100, with labels at every 10 numbers. It may go from 0 to 1, with labels at every 0.1.
- Plot the data points. The first column of data relates to the data point’s orientation along the X axis. The second column relates to its orientation along the Y axis. For example, if the data point is (3,5), it should be plotted 3 units to the right of the point where the X and Y axis cross, and five units up. Each point should be represented by a small dot or X mark. If you have two sets of data that are not already written in the form of (3,5), the horizontal axis should be the independent variable, or the one you think caused the other. The vertical axis is the dependent variable, or the one you think was caused by the other set of data.
- View the results. If the results seem closely grouped along a line or parabola (U or V shape), there is a strong correlation between the two sets of data. If they do not seem to be related, the association between the two sets of data is weak, or there may be no correlation at all. If they are strongly correlated and form a sharp slope, then a change in the first variable greatly affects the second variable. If the slope is nearly flat (horizontal), a large change in the first variable will only affect the second variable a little.
The scatter diagram or scatter plot is often used in algebra classes, but there are many real world applications. For example, one might plot the hours of sleep students receive the night before an exam with their score on the exam to see if amount of sleep seems to cause a change in exam score.