Principal component analysis is a variable reduction procedure. It is useful when you have
obtained data on a number of variables (possibly a large number of variables), and believe that
there is some redundancy in those variables. In this case, redundancy means that some of the
variables are correlated with one another, possibly because they are measuring the same
construct. Because of this redundancy, you believe that it should be possible to reduce the
observed variables into a smaller number of principal components (artificial variables) that will
account for most of the variance in the observed variables.