Correlation Flashcards
What are 3 obstacles to experimentation?
Ethical (harmful), credibility and practical (can’t manipulate) problems
What is the full name for r?
Pearson product-moment correlation coefficient
What is r? (What is another name)
An index of strength of relationship between two variables (aka zero-order correlation)
What typifies a correlation of 0?
No relationship - No tendency for a higher score on one to be associated with a higher or lower score on the other; the mean is the best predictor.
What is the numerator in covariance ?
The summed products of deviation scores.
Why is covariance dependent on the scale of the measured variables?
Because it is not standardised (taking into account z scores)
What does a test for the significance of r reveal?
Whether the linear relationship exists in the population, or if its likely due to sampling error.
What is rho?
The correlation coefficient in the population
What is the population correlation coefficient (rho) under the null hypothesis?
0, and it is normally distributed.
What are the degrees of freedom when testing significance of r?
N-2
What happens to the significance of r as N increases?
Smaller r values can reach significance
What size of r value would be significant for N= 52 and N=102?
.27 & .19
What is k^2? What does it refer to?
The coefficient of non-determination, or 1-r^2. Amount of variance that cannot be predicted by the other variable (residual/error).
When would you use point-biserial correlation?
When one variable is genuinely dichotomous, having 2 levels. (Yes/no, present/absent, left/right, etc)
What can affect the sign of a correlation using point-biserial?
How the dichotomous variable is labelled. Swapping 0 and 1 results in inverting the sign.
