Correlation basics
What does a correlation measure?
➡️ The relationship between two variables.
What does the sign (+ or –) in a correlation coefficient tell us?
It shows whether the relationship is positive or negative.
There’s a positive correlation between hours studied and test scores. What does this mean?
Students who study more tend to get higher scores.
What kind of data do you need to calculate a correlation?
Numerical (quantitative) data.
True or False: A strong correlation always means one variable causes the other.
False
What does a positive correlation mean?
➡️ As one variable increases, the other also increases.
What does the number part of a correlation coefficient tell us?
It shows how strong the relationship is between two variables.
There’s a negative correlation between time spent watching TV and grades. What does this mean?
As TV time goes up, grades tend to go down.
What type of graph is most often used to show correlations?
A scatterplot.
What phrase should you always remember when interpreting correlations?
Correlation does not equal causation
What does a negative correlation mean?
As one variable increases, the other decreases.
If two variables have a correlation of +0.90, what does that mean?
They have a very strong positive relationship.
If ice cream sales and sunburns are positively correlated, what’s likely causing both?
Hot weather (a third variable).
What kind of correlation is shown when data points go down from left to right?
A negative correlation.
If you find that stress and poor sleep are correlated, what should you investigate next?
Which one might cause the other — or if something else causes both.
What does a correlation of 0 mean?
There is no relationship between the variables.
If two variables have a correlation of -0.75, what does that mean?
They have a strong negative relationship.
What’s an example of two variables that are correlated but not causally related?
Number of pirates and global temperature (a spurious correlation).
What kind of correlation is shown when data points go up from left to right?
A positive correlation
What type of study uses correlation to analyze variables without manipulating them?
Observational study.
What is the main difference between correlation and causation?
Correlation shows a relationship, but not cause and effect.
What is the difference between a strong correlation and a weak correlation?
A strong correlation means the variables are closely related, while a weak correlation means they are only slightly related.
What’s the term for when two variables seem related but are both influenced by another factor?
A third-variable problem.
What kind of correlation is shown when the data points are random with no pattern?
No correlation.
Why do researchers use correlation before experiments?
To identify possible relationships worth studying further.