Measures of Association (Lecture 8) Flashcards
What do measures of association consider?
The relationship between two variables
What data do we use when we want to look at the measure of association?
categorical or continuous data
What test is associated with categorical data?
Chi-squared (x2)
What test is associated with continuous data?
Pearson’s correlation coefficient (r)
What does chi-squared test show?
If there are differences between the expected and observed values
What does correlation represent?
The strength and magnitude of the association between two variables
What does the correlation coefficient r range from?
-1 to 1 (zero means no association), (positive is 0-1), (negative is -1 to 0)
What tables are used for calculating chi-squared?
Contingency tables
What is the critical value?
How far from the expected centre do you need to be before we can say ‘there’s something unusual here’
What is data is used for correlation?
Continuous data
What does positive covariance indicate?
Variables that tend to move together away from their means
What does negative covariance indicate?
Variables that move in opposite directions
What does correlation coefficient range from?
-1 to 1
What plots are used with the correlation coefficient?
Scatter plots
What do scatter plots check?
If you are examining a linear relationship
What can strengthen the correlation coefficient?
Outliers or a ‘missing middle’
What is a strong correlation r value?
r = ±0.8
What is a weak correlation r value?
r = ±0.3
True or False: Can variables be strongly associated with one another without any casual relationship?
True
What’s an omitted variable?
A third factor could lead to changes in X and Y
What’s reverse causality?
A change in Y leads to the change in X
What’s sample selection bias?
Individuals sampled have a different tendency to show the association than the whole population
What’s measurement error?
Values in the data differ from the true value of the variable
What does association not imply?
Causation
