Correlation

• Correlation means association - it is a measure to the extent to which two variables are related

  One of the variables can be regarded as the predictor variable whereas the other can be seen as the outcome variable
• Correlational studies involve two different measures from a group of participants and then assessing the degree of association between the measures
• Predictor variable 


  Can be seen as occurring before the outcome variable in some sense

  Called the predictor because it forms the basis for predicting the value of the outcome variable
• Relationships between the variables can be seen on a graph or as a numerical score called the correlation coefficient.
• If an increase in one variable tends to be associated with an increase in the other, then this is known as a positive correlation
• If an increase in one variable tends to be associated with a decrease in the other, then this is known as a negative correlation
• A zero correlation occurs when there is no relationship between variables
• Spearman’s rho


  Statistical test of correlation

  The test will give us a correlation coefficient.

  This is a value between 0 and 1, and the closer to 1 the score is, the stronger the relationship between the variables

  This value can be both positive
• Correlation does not always prove causation, as a third variable may be involved.
• A correlation between variables, however, does not automatically mean that the change in one variable is the cause of the change in the values of the other variable
• Closer the data points are to the line of best on a scatter graph , the stronger the correlation

  Can be measured numerically using a correlation coefficient
• Curvilinear correlations often look like a bell curve
• Correlations never prove causation as other variables could have caused the relationship , these are called intervening variables