Graphs from Peck, Olsen, Devore
Page 2 of 4
_____________________________________________________________!
Just because
two variables have a strong correlation does not mean that one causes the other
—
there may be an alternative explanation including chance.
Do storks cause babies?
Stork population vs. babies born

in a small town in
Germany, both populations increased over time
Does smoking cause cancer?
—
difficult to prove although correlation exists
•
_________________________
—
general term, often used for categorical variables
as well as numeric;
•
_________________________
only applies to _____________________ variables
and is a statistical ____________________________________________________
___________________________________________________________________
___________________________________
—
a variable other than the two we are studying
(x and y) that influences both variables of interest, explaining the relationship
between the two (often a _____________________________
—
ice cream sales and
number of people who drown both respond to hot weather)
___________________________________
—
two variables are confounded when their
___________________________________________________________________
__________________________________________________________; difficult to
determine whether either of them is causal