Correlations

• Statistical tests of correlation produce a numerical value somewhere between -1 and 1. This is the correlation coefficient. The correlation coefficient is a measure of the strength of the relationship between two variables.
• The closer the correlation coefficient is to 1, the stronger the relationship between the 2 variables.
• Value of +1 represents a perfect positive correlation.
• Value of -1 represents a perfect negative correlation.
• Correlation coefficients are calculated using an inferential test, such as Pearson's r.
• Types of correlation

  
• A correlation is a test of association between two co-variables whereas an experiment is a test of difference between two co-variables.