Correlation Flashcards
For each statistical analysis, we have what same elements?
- Data (from which we calculate…)
- Test statistic (represents the relationship of interest, which we compare to…)
- Distribution of that test statistic under the null hypothesis (to get…)
- Probability p of getting test statistic as large as the on e we have or larger if the null hypothesis is true (so we can…)
- Evaluate our competing hypotheses using a perviously decided alpha level
What does a correlation do?
Quantifies how two quantities change in relation to each other
Define variance
How do you calculate it?
How much scores deviate from the mean, on average
Calculate how far each data point is from the mean of x, multiply the deviations by themselves, add them all together, divide by N - 1
Define covariance
How do you calculate it?
How much pairs of scores deviate from their (respective) means in the same way, on average
Calculate how far each data point is from the mean for both x and y, multiply them together, add all those together, divide by N - 1
What is meant by the signal?
The effect or relationship of interest
r quantifies the strength and direction of the relationship
What values is r always between?
What types of variables is it typically used with?
ALWAYS has a value between -1 and 1
Typically used with two (or more) continuous variables, can be used when one is categorical
In regards to r, what is strength?
Absolute value of r between 0 and 1
In regards to r, what is direction?
The sign of r (positive or negative)
Define tertium quid
An unmeasured third variable that influences two other measured quantities
Define correlation in a statistical context
The (standardised) degree to which two variables covary. Calculated as covariance divided by the product of the standard deviations. Quantifies both the strength (absolute value) and direction (sign) of the relationship between -1 and 1.
