What is a Correlation?
A correlation is a measure of the association / relationship between two variables.
Image credit: http://www.abacon.com/slavin/t2.html
A correlation does not imply causation.
The video below provides a good explanation on what a correlation is.
The video below provides a good explanation on what a correlation is.
Correlation values can range from -1 to +1.
The correlation coefficient (r) reflects the amount of variability shared between two variables.
The more they have something in common, the larger the r.
The r (also known as the Pearson correlation) can be calculated using the formula below. Else, you can just use SPSS and get it with a click of a button :)
Image credit: http://ordination.okstate.edu/STATS.htm
The correlation coefficient (r) reflects the amount of variability shared between two variables.
The more they have something in common, the larger the r.
The r (also known as the Pearson correlation) can be calculated using the formula below. Else, you can just use SPSS and get it with a click of a button :)
Image credit: http://ordination.okstate.edu/STATS.htm
Want to see how the above formula works, click on the link below:
http://www.statisticshowto.com/articles/how-to-compute-pearsons-correlation-coefficients/
http://www.statisticshowto.com/articles/how-to-compute-pearsons-correlation-coefficients/
Variance Explained
By squaring the r, we get what is known as the Coefficient of Determination - which gives us the amount of variance explained.
If for example,
Depression is our DV (Dependent Variable)
Bullying is our IV (Independent Variable)
And from our data, we calculate r=0.3. Then our r-square is 0.09.
Meaning 9% of that variance in depression that we measured in our kids in school can be explained by their experience of being bullied.
(Still, this is not causation, as there could be a third unmeasured variable)
If for example,
Depression is our DV (Dependent Variable)
Bullying is our IV (Independent Variable)
And from our data, we calculate r=0.3. Then our r-square is 0.09.
Meaning 9% of that variance in depression that we measured in our kids in school can be explained by their experience of being bullied.
(Still, this is not causation, as there could be a third unmeasured variable)