The Box Plot

Boxplots

Boxplots can be used to explore distribution of one continuous variable for the whole sample or, alternatively, the researcher can search for scores to be disagregated by different groups. The output from boxplot gives the researcher a lot of information about the distribution of the continuous variable and the possible influence of the categorical variable. A boxplot allows the researcher to inspect a pattern of scores within each group and allows visual inspection of the differences between groups (Pallant, 2016).

Contributed by Joseph W. Sullivan

Creating a box and whisker plot using SPSS

(Refer to emailed file for screen-shots and further assistance)

1) Open SPSS and EXCEL

2) Copy the data (into SPSS) that you would like to use. For example, test scores disaggregated by gender. Make sure that you assign numbers to gender (In example below: 1 = male; 2 = female).

3) Once data is entered into SPSS (as depicted above), click on: “Graphs  boxplot”

4) Click “define” (with “simple” & “summary for groups of cases” chosen)

5) Move “test” (or your variable of choice) into the variable section

6) Move “gender” (or whatever you choose) into the “category axis” section.

7) Click OK.

8) In order to format in APA, double click on the graph in SPSS. Change each axis to read what you would like them to read.

9) Close the “chart editor” and copy and paste your final graph from SPSS into your document of choice.

10) Have a drink to congratulate yourself on a job well done. Please note: this step is not in the latest version of APA).

contributed by Chris Longo

What is a Box Plot and When is It Used

The box plot or box-and-whisker plot is a graphic, created by John W. Tukey, used to show the distribution of a set of data. It is frequently used with data that can also be represented with a histogram, but the box plot shows more information than a standard histogram. For example, the box plot is useful to researchers because it shows extreme scores.

How to Read a Box Plot

Let's say we ask 282 people how many pairs of shoes they've consumed in the past ten years. We'll sort those responses from least to greatest and then graph them with our box-and-whisker. See the example above.

Take the top 50% of the group (142) who bought more pairs of shoes; they are represented by everything above the median (the white line). Those in the top 25% of shoe buying (71) are shown by the top "whisker" and dots. Dots represent those who bought a lot more shoes than normal or a lot less than normal (outliers). If more than one outlier bought the same number of shoes, dots are placed side by side.

contributed by Michael Minzloff

How-to Video

How to create a box and whisker plot using SPSS [1]

contributed by Jen Eraca