Correlation Flashcards
3 questions in correlation
- Are the variables related to each other?
- What is the direction of the relationship?
- What is the strength of the relationship?
If variables are related
A change in a variable corresponds to a change in the other variable
What direction can a cor-relational relationship be
Positive
Negative
What indicates the strength of a correlation
The absolute value of the relationship
What to look for in a scatterplot
Do the scores resemble a straight line or a cluster?
If its a straight line, what is the direction
Residual
Correlation error
Covariance
Measures the degree that two variable move together
Negative covariance
As one variable up, other goes down
Positive covariance
Both variables go up
Covariance equation
Sum of cross-products/divided by N
(x-x’)(y-y’)/N
Variance
Extent that a variable moves by itself
Drawbacks with using covariance
Absolute value is impacted by the scale of measurement used
Unrelaible index of the size of the relationship between variables
How can we resolve the issue with covariance
Convert the scores to z-scores
What di z-scores tell
How above or below someone is of the mean in a standard distribution
Tells relative position not absolute position
Key properties of z- distribution
- Mean of zero
2. Standard deviation of 1
