The pooled estimated standard deviation is obtained by adding together
the residual sum of squares for each non-null element of
object
, dividing by the sum of the corresponding residual
degrees-of-freedom, and taking the square-root.
USAGE:
pooledSD(object)
REQUIRED ARGUMENTS:
object
an object inheriting from class
lmList.
VALUE:
the pooled standard deviation for the non-null elements of
object
, with an attribute
df with the number of
degrees-of-freedom used in the estimation.