A scatterplot is one way to check for outliers-look for points that are far away from the others. The data have no outliers : Outliers are observations that don’t follow the same patterns as the rest of the data.It’s not a problem if the variables are a little non-normal. The variables are normally distributed : You can create a histogram of each variable to verify whether the distributions are approximately normal.Both variables are quantitative : You will need to use a different method if either of the variables is qualitative.The Pearson correlation coefficient is a good choice when all of the following are true: The Pearson correlation coefficient ( r) is one of several correlation coefficients that you need to choose between when you want to measure a correlation. When to use the Pearson correlation coefficient When r is 0, a line of best fit is not helpful in describing the relationship between the variables: 3 or between 0 and –.3, the points are far from the line of best fit: 5 or less than –.5, the points are close to the line of best fit: When r is 1 or –1, all the points fall exactly on the line of best fit: When the slope is positive, r is positive. When the slope is negative, r is negative. The Pearson correlation coefficient also tells you whether the slope of the line of best fit is negative or positive. Try for free Visualizing the Pearson correlation coefficientĪnother way to think of the Pearson correlation coefficient ( r) is as a measure of how close the observations are to a line of best fit. Specifically, we can test whether there is a significant relationship between two variables. The Pearson correlation coefficient is also an inferential statistic, meaning that it can be used to test statistical hypotheses. Specifically, it describes the strength and direction of the linear relationship between two quantitative variables.Īlthough interpretations of the relationship strength (also known as effect size) vary between disciplines, the table below gives general rules of thumb: Pearson correlation coefficient ( r) value The Pearson correlation coefficient is a descriptive statistic, meaning that it summarizes the characteristics of a dataset. Pearson product-moment correlation coefficient (PPMCC). The Pearson correlation coefficient ( r) is the most widely used correlation coefficient and is known by many names: What is the Pearson correlation coefficient?
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