Descriptive Statistics > Scatter Plot / 3D Scatter Chart
What is a Scatter Plot?
Scatter plots are similar to line graphs. A line graph uses a line on an X-Y axis to plot a continuous function, while a scatter plot uses dots to represent individual pieces of data. In statistics, these plots are useful to see if two variables are related to each other. For example, a scatter chart can suggest a linear relationship (i.e. a straight line).
The relationship between variables is called correlation. Correlation is just another word for “relationship.” For example, how much you weigh is related (correlated) to how much you eat. In statistics, there are two type of correlation: positive correlation and negative correlation. If data points make a line from the origin from low x and y values to high x and y values the data points are positively correlated, like in the above graph. If the graph starts off with high y-values and continues to low y-values then the graph is negatively correlated.
You can think of positive correlation as something that produces a positive result. For example, the more you exercise, the better your cardiovascular health. “Positive” doesn’t necessarily mean “good”! More smoking leads to more chance of cancer and the more you drive, the more likely you are to be in a car accident.
Simple scatter plots are fairly easy to draw by hand, especially if you have very few data points. However, in real life, you’re likely to have very large sets of data to work with. If you want to use technology to graph the plot you have several options:
- How to Make a Scatter Plot in Microsoft Excel.
- How to Make a TI 83 Scatter Plot.
- How to Make a Scatter Plot on the TI 89 Calculator.
- How to Make an SPSS Scatterplot.
Scatter plots are also called scattergraphs, scatter charts, scatter diagrams and scattergrams.
3D Scatter Plot
A 3D scatter plot is a scatter plot with three axes. For example, the following 3D scatter plot shows student scores in three subjects: Reading (y-axis), Writing (x-axis) and Math (z-axis).
Student A scored 100 in Writing and Math and 90 in reading, and student B scored 50 in writing, 30 in reading and 15 in math. 3D plots are fairly easy to make for a few points, but once you start to get into larger sets of data, you’ll want to use technology. Unfortunately, Excel doesn’t have an option to create these chart. Statistical programs commonly available through colleges and universities (like SAS) can create them. There are quite a few free options available, but I recommend:
- Plotly is an easy way to create a 3D chart online.
- Gnuplot: downloadable program. Easy to use compared to other programs.
- R: Also a download. Has a fairly steep learning curve, but handles most statistical computations. If you want a general stst package (As opposed to one that will just create charts), this is the best option.