## Type III Tests

The **Type III Tests** table presents the Type III sums of
squares associated with the estimated coefficients in the model.
Type III sums of squares are commonly called partial sums of
squares (for a complete discussion, refer to the chapter titled
"The Four Types of Estimable Functions"
in the *SAS/STAT User's Guide*).
The Type III sum of squares for a particular variable
is the increase in the model sum of squares due to
adding the variable to a model that already contains
all the other variables in the model.
Type III sums of squares, therefore, do not depend on the order
in which the explanatory variables are specified in the model.
Furthermore, they do not yield an additive partitioning of
the **Model** sum of squares unless the explanatory variables
are uncorrelated (which they are not for this example).
*F* tests are formed from this table as
explained previously in the "Analysis of Variance" section.
Note that when **DF = 1**, the Type III *F* statistic
for a given parameter estimate is equal to the square
of the *t* statistic for the same parameter estimate.
For example, the **T Stat** value for **HSM** given in the
**Parameter Estimates** table is **4.7494**.
The corresponding **F Stat** value in the **Type III Tests**
table is **22.5569**, which is **4.7494** squared.

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