The correlation analysis is used to measure the direction and relationship between two variables. It's important to note that correlation does not equal causation. That means that while a relationship may be observed, it's impossible to say that one variable caused or affected the other variable. The relationship observed may be due to other variables not accounted for in the model.
Research Question & Hypotheses Examples
RQ: What is the relationship between height and age?
RQ: Is there a significant linear relationship between hours of exercise and weight?
The direction of the relationship can be assessed by looking at the sign of the correlation coefficient.
The strength of the relationship can be assessed by evaluating the numerical value of the correlation coefficient. Correlation values can range from -1 to +1.
The measure of effect size used for correlation analyses is called the coefficient of determination or R-Squared. This value can be found by simply squaring the value of the correlation coefficient (r). For example, if r = .3, then the effect size is .09. This is interpreted as saying that 9% (.09 x 100 = 9%) of the variability in one variable is explained by the other variable.
See the Correlation page for additional information