Lecture 8A: Pearson’s Correlations Flashcards
What is Pearson’s r also known as?
Pearson’s correlation coefficient
What type of relationship does Pearson’s r describe?
The linear relationship between two continuous variables.
What does a positive correlation indicate?
X and Y go in the same direction.
What does a negative correlation indicate?
X and Y go in the opposite direction.
What is the range of values for Pearson’s r?
Absolute magnitude of 0 to 1, where the higher the absolute value, the stronger the relationship
What does a value of r = +1.00 indicate?
Perfect positive correlation.
What does a value of r = -1.00 indicate?
Perfect negative correlation.
What does a value of r = 0 indicate?
No correlation.
What is the significance of data points being closer to a straight line in relation to Pearson’s r?
It indicates a stronger strength of correlation.
What is the convention for interpreting the strength of Pearson’s r values?
- 0.00-0.25: little or no correlation
- 0.25-0.50: fair correlation
- 0.50-0.75: moderate to good correlation
- > 0.75: good to excellent correlation
What are the criteria for using Pearson’s r?
- Interval or ratio data (continuous)
- Linear relationship (e.g. scatter plot)
- Normal distribution
- Each subject must provide data for both variables.
How does sample size affect Pearson’s r?
The critical value of r changes with sample size.
What major factor can affect the value of r?
- Range of data: Greater range (sample size), greater r value
- Measurement error
- Non-linear relationships
- Outliers: cause over/underestimation
What happens to r if there is a greater measurement error?
The value of r decreases.
What should you do when outliers affect your correlation analysis?
- Recruit more subjects
- Remove the outlier based on specific criteria.
True or False: Pearson’s r can establish causality between two variables.
False.
What does Pearson’s r only tell you in a cross-sectional study?
Whether the two variables are correlated or not.
