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Statistics guide for graphpad prism 89/21/2023 Correlation asks how much X and Y vary together. If all Y values are the same, it is not possible to compute a correlation coefficient (parametric or nonparametric), and Prism reports "horizontal line".It does not compute multiple regression, or partial regression, coefficients. If you ask Prism to compute a correlation matrix (compute the correlation coefficient for each pair of variables), it computes a simple correlation coefficient for each pair, without regard for the other variables.So with smaller n, Prism simply does not report the confidence interval of the Spearman correlation coefficient. According to Zar (Biostatistical Analysis) this approximation should only be used when n>10. If you choose Spearman nonparametric correlation, Prism computes the confidence interval of the Spearman correlation coefficient by an approximation.The P value quantifies the likelihood that this could occur. X and Y don’t really correlate at all, and you just happened to observe such a strong correlation by chance.Changes in another variable influence both X and Y.Changes in the Y variable causes a change the value of the X variable.Changes in the X variable causes a change the value of the Y variable.If r or rs is far from zero, there are four possible explanations: One variable increases as the other decreases. The two variables do not vary together at all. The two variables tend to increase or decrease together.
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