In this post you will learn how to create a scatter plot in spss.
Scatter Plot –
Sometimes we need to look at the relationship between variables (rather than their means or frequencies). A Scatter plot is a graph that plots each person’s score on one variable against their score on another. It tells us whether there seems to be a relationship between the variables, what kind of relationship it is and whether any cases are markedly different from the others. Creating a scatter plot in spss is very easy.
Let’s create a scatter plot in spss. But first download the dataset that we are going to use in this post – click here to download.
Open spss and go to Files > open > data. And select the data that you have downloaded. It will look like this –
To create a scatter plot in spss, go to Graphs > chart builder. In the chart builder select scatter/Dot in the list labelled choose from in the Gallery tab as shown below.
This gallery has eight icons representing different types of scatter plot and you should select the appropriate one by either double-clicking on it or dragging it into the canvas.
- Simple scatter – Use this option when you want to plot values of one continuous variable against another.
- Grouped Scatter – This is like a simple scatter plot, except that you can display points belonging to different groups in different colors (or symbols)
- Simple 3-D scatter – Use this option to plot values of one continuous variable against values of two others.
- Grouped 3-D scatter – Use this option if you want to plot values of one continuous variable against two others but differentiating groups of cases with different colored dots.
- Summary point plot – This graph is same as a bar chart, except that a dot is used instead of a bar.
- Simple dot plot – otherwise known as a density plot, this graph is similar to a histogram, except that rather than having a summary bar representing the frequency of scores, a density plot shows each individual scores as a dot.
- Scatterplot matrix – This option produces a grid of scatter plots showing the relationship between multiple pairs of variables.
- Drop-line – This option produces a graph that is similar to a clustered bar chart but with a dot representing a summary statistics (e.g. the mean) instead of bar and with a line connecting means of different groups. This can be useful for comparing statistics such as mean, across different groups.
Simple Scatter Plot –
This type of scatter plot is for looking at just two variables. For example, a psychologist was interested in the effects of exam stress on exam performance. So, she devised and validated a Questionnaire to access state anxiety relating to exams. This scale produced a measure of anxiety scored out of 100. Anxiety was measured before an exam and the percentage mark of each student on the exam was used to assess the exam performance.
In the chart builder double-click on the icon for a simple scatter plot with fit line. On the canvas you will see a graph and two drop zones. one for the y-axis and one for the x-axis. The y-axis needs to be the dependent variable(the outcome that was measured). In this case the outcome is Exam Performance (%), so select it from the variable list and drag it into the y-axis drop zone.
The horizontal axis should display the independent variable ( the variable that predicts the outcome variable). In this case it is Exam Anxiety, so click on this variable in the variable list and drag it into the drop zone for the x-axis. The dialog box should look like this –
Click on OK to create the scatter plot.
The scatter plot tells us that the majority of students suffered from high level of anxiety (there are very few cases that had anxiety levels below 60). Also there are no obvious outliers in that most point seem to fall within the vicinity of other points. There also seems to some trend in the data shown by the line such that higher level of anxiety are associated with lower exam scores and low level of anxiety are almost always associated with high examination marks. Another noticeable trend in these data is that there were no cases having low anxiety and low exam performance- in fact most of the data are clustered in the upper region of the anxiety scale.
Grouped Scatter plot –
What if we want to see whether male and female students had different reactions to exam anxiety? To do this, we need a grouped scatter plot. This type of scatter plot is for looking at two continuous variables but when you want to color data points by a third categorical variable. Sticking with our previous example, we could look at the relationship between exam anxiety and exam performance in males and females (our grouping variable).
To do this we double click on the grouped scatter icon in the chart builder. As in the previous example, we select Exam performance (%) from the variable list and drag it into the y-axis drop zone and select Exam Anxiety and drag it into x-axis drop zone. There is an additional drop zone set color into which we can drop any categorical variable. In this case, Gender is the only categorical variable in our variable list, so select it and drag it into this drop zone. Then select the subgroup in the linear fit line at the right bottom.
The dialog box will look like this –
Click on OK to create the grouped scatter plot.
These lines tell us that the relationship between exam anxiety and exam performance was slightly stronger in males (the line is steeper) indicating that men’s exam performance was more adversely affected by anxiety than women’s exam performance.