Graphs from Peck, Olsen, Devore
Page 2 of 4
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