correlation analysis deals with the _between two or more variable
Answers
Correlation tests look for an association between (two) variables. A positive correlation is one in which, as one variable increases the other one increases. A negative correlation is one in which, as one variable increases the other one decreases.
Correlation tests determine if this association is statistically significant.*
Pearson correlation is most appropriate when the relationship between the two variables is linear.
Spearman and Kendall correlation tests do not assume that the relationship is linear. Instead the they use the ranks of values. So that, an S-shaped curve could have a high correlation by Spearman or Kendall.
There are other correlation tests for more specific situations, such as the linear-by-linear test for ordinal data.
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* This is a concept that should be understood before using these tests.