Running A Point Biserial Correlation In Spss
For example, you could use a point-biserial correlation to determine whether there is an association between salaries, measured in US dollars, and gender (i.e., your continuous variable would be "salary" and your dichotomous variable would be "gender", which has two categories: "males" and "females"). Alternately, you could use a point-biserial correlation to determine whether there is an association between cholesterol concentration, measured in mmol/L, and smoking status (i.e., your continuous variable would be "cholesterol concentration", a marker of heart disease, and your dichotomous variable would be "smoking status", which has two categories: "smoker" and "non-smoker").
running a point biserial correlation in spss
This "quick start" guide shows you how to carry out a point-biserial correlation using SPSS Statistics, as well as how to interpret and report the results from this test. However, before we introduce you to this procedure, you need to understand the different assumptions that your data must meet in order for a point-biserial correlation to give you a valid result. We discuss these assumptions next.
When you choose to analyse your data using a point-biserial correlation, part of the process involves checking to make sure that the data you want to analyse can actually be analysed using a point-biserial correlation. You need to do this because it is only appropriate to use a point-biserial correlation if your data "passes" five assumptions that are required for a point-biserial correlation to give you a valid result. In practice, checking for these five assumptions just adds a little bit more time to your analysis, requiring you to click a few more buttons in SPSS Statistics when performing your analysis, as well as think a little bit more about your data, but it is not a difficult task.
You can check assumptions #3, #4 and #5 using SPSS Statistics. Just remember that if you do not run the statistical tests on these assumptions correctly, the results you get when running a point-biserial correlation might not be valid.
In the section, Procedure, we illustrate the SPSS Statistics procedure to perform a point-biserial correlation assuming that no assumptions have been violated. First, we set out the example we use to explain the point-biserial correlation procedure in SPSS Statistics.
The Correlate > Bivariate... procedure below shows you how to analyse your data using a point-biserial correlation in SPSS Statistics when none of the five assumptions in the previous section, Assumptions, have been violated. After this procedure, we show you how to interpret the results from this test.
Since some of the options in the Correlate > Bivariate... procedure changed in SPSS Statistics version 27 and the subscription version of SPSS Statistics, we show how to carry out a point-biserial correlation depending on whether you have SPSS Statistics version 27 or 28 (or the subscription version of SPSS Statistics) or version 26 or an earlier version of SPSS Statistics. The latest versions of SPSS Statistics are version 28 and the subscription version. If you are unsure which version of SPSS Statistics you are using, see our guide: Identifying your version of SPSS Statistics.
Now that you have run the Correlate > Bivariate... procedure to carry out a point-biserial correlation, go to the Interpreting Results section. You can ignore the section below, which shows you how to carry out a point-biserial correlation if you have SPSS Statistics version 26 or an earlier version of SPSS Statistics.
If your data passed assumptions #3 (no outliers), #4 (normality) and #5 (equal variances), which we explained earlier in the Assumptions section, you will only need to interpret the Correlations table. Remember that if your data failed any of these assumptions, the output that you get from the point-biserial correlation procedure (i.e., the table we discuss below), will no longer be correct.
However, in this "quick start" guide, we focus on the results from the point-biserial correlation procedure only, assuming that your data met all the relevant assumptions. Therefore, if you ran the point-biserial correlation procedure in the previous section using SPSS Statistics version 27 or the subscription version of SPSS Statistics, you will be presented with the Correlations table below:
The Correlations table presents the point-biserial correlation coefficient, the significance value and the sample size that the calculation is based on. In this example, we can see that the point-biserial correlation coefficient, rpb, is -.358, and that this is statistically significant (p = .023).
If you are looking for "Point-Biserial" correlation coefficient, just find the Pearson correlation coefficient. In SPSS, click Analyze -> Correlate -> Bivariate. The rest is pretty easy to follow. Computationally the point biserial correlation and the Pearson correlation are the same.
Point-biserial correlation is used to understand the strength of the relationship between two variables. Your variables of interest should include one continuous and one binary variable. See more below.
The variables that you care about must not contain outliers. Point-Biserial correlation is sensitive to outliers, or data points that have unusually large or small values. You can tell if your variables have outliers by plotting them and observing if any points are far from all other points.
How do I run Point-Biserial Correlation in SPSS or R?A: StatsTest is focused on helping you pick the right statistical method every time. There are many resources available to help you figure out how to run this method with your data:SPSS article: -tutorials/point-biserial-correlation-using-spss-statistics.phpSPSS video: =76ipx-ta8FYR article: -1/topics/biserial.cor
Methods: A cross-sectional survey was conducted among students studying in different universities of Islamabad and Rawalpindi belonging to both public and private sectors. The study was conducted between May 2018 and March 2019. Sample size was 360 students which were selected through convenience sampling. Data was collected through self-formulated closed ended questionnaire. Patient Rated Wrist Evaluation questionnaire was used to assess pain and disability at wrist joint. Data entry and analysis were done using SPSS 21. Results were analyzed using descriptive statistics. Spearman's and point-biserial correlation coefficients were applied to determine association between different variables.
A high point-biserial reflects the fact that the item is doing a good job of discriminating your high-performing students from your low-performing students. Values for point-biserial range from -1.00 to 1.00. Values of 0.15 or higher mean that the item is performing well (Varma, 2006). According to Varma, good items typically have a point-biserial exceeding 0.25. Items with incorrect keys will show point-biserials close to or below zero. As a rule of thumb, items with a point-biserial below 0.10 should be examined for a possible incorrect key.
Point-biserials that are negative signal a big problem. With this pattern, the high-performing students are getting the answer wrong, and the low and/or mid performing students are getting it right. Researchers have recommended removing items that have a negative point-biserial (Kaplan & Saccuzzo, 2013).
The content from this post was provided courtesy of Jennifer Balogh Ph.D. To learn more about point-biserial and other tips to create the best exams possible, pick up A Practical Guide to Creating Quality Exams by J Balogh. Jennifer has been in the testing industry for over a decade and owns a consulting business dedicated to designing, developing, and accurately scoring tests.
There is a simple difference formula to compute the rank-biserial correlation from the common language effect size: the correlation is the difference between the proportion of pairs favorable to the hypothesis (f) minus its complement (i.e.: the proportion that is unfavorable (u)). This simple difference formula is just the difference of the common language effect size of each group, and is as follows:
For example, consider the example where hares run faster than tortoises in 90 of 100 pairs. The common language effect size is 90%, so the rank-biserial correlation is 90% minus 10%, and the rank-biserial r = 0.80.