10Hmmmm….Do NOT confuse association, correlation and causation.
11AssociationDeliberately vague term to describe the relationship between two variables.This can be used for CATEGORICAL dataEx: Did you know there’s a strong correlation between playing an instrument and drinking coffee…. NO. It’s an association!
12CorrelationPrecise term describing the strength and direction of the linear relationship between quantitative variables.
13CausationScatterplots and correlation coefficients NEVER prove causation.This is why it is so hard to prove something causes something else– for example, just because lung cancer and smoking is correlated doesn’t mean that one causes the other and when considering one causing the other you need to consider both.Does smoking cause cancer?ORDoes cancer cause smoking?You need to do further tests to actually figure this out.
14Example 1A news reporter claims “There appears to be a strong correlation between whether you own a pet and the condition of a person’s yard.”Thoughts on this?
15Example 2:A researcher studies children in elementary school and finds a strong positive linear association between height and reading scores.Does this mean that taller readers are generally better readers?What might explain the strong correlation?
16What is wrong? Example 3The correlation coefficient between Olympic gold medal times for the 800 m hurdles and year is seconds per year.
18What’s wrong? Example 4The correlation coefficient between Olympic Gold Medal times for the 100m dash and year is -1.37
19AnswerCorrelation Coefficient of is impossible! Correlation coefficient will always be between -1 and 1!
20What’s Wrong? Example 5Since the correlation coefficient between Olympic gold medal times for the 800m hurdles and 100m dash is -0.41, the correlation coefficient between times for the 100m dash and the 800m dash hurdles will be 0.41
21AnswerCorrelation does not change if we reverse x and y variables.
22What’s Wrong?- Example 6If we were to measure Olympic gold medal times for the 800m hurdles in minutes instead of seconds, the correlation coefficient would be -.66/60 =
23AnswerCorrelation does not change when we change units!
24Practice Problems Try some on your own! As always call me over if you are confused!
25Exit Ticket Explain the error: Your friend claims that the correlation coefficient between what continent you live on and how many hours you sleep is