<!doctype s-function-doc system "s-function-doc.dtd" [
<!entity % S-OLD "INCLUDE">
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<s-function-doc>
<s-topics>
   <s-topic>drop1.lmRob</s-topic>
</s-topics>

<s-title>
Compute an Anova Object by Dropping Terms 
</s-title>

<s-description>
<s-expression>drop1.lmRob</s-expression> is used to investigate a robust Linear Model object by  
recomputing it, successively omitting each of a number of specified terms. 
</s-description>

<s-usage>
<s-old-style-usage>
drop1.lmRob(object, scope, scale, keep, fast = F, ...) 
</s-old-style-usage>
</s-usage>

<s-args-required>
<s-arg name="object">
an <s-expression>lmRob</s-expression> object. 
</s-arg>
</s-args-required>

<s-args-optional>
<s-arg name="scope">
an optional <s-expression>formula</s-expression> object describing the terms to be dropped. Typically  
this argument is omitted, in which case all possible terms are dropped  
(without breaking hierarchy rules). The <s-expression>scope</s-expression> can also be a character  
vector of term labels. If the argument is supplied as a formula, any <s-expression>"."</s-expression>  
is interpreted relative to the formula implied by the <s-expression>object</s-expression> argument. 
</s-arg>

<s-arg name="scale">
an estimate of the scale of the residuals. If not supplied, the initial  
estimate of the scale in <s-expression>object</s-expression> is used. 
</s-arg>

<s-arg name="keep">
a character vector of names of components that should be saved for each  
subset model. Only names from the set <s-expression>"coefficients"</s-expression>, <s-expression>"fitted"</s-expression> and  
<s-expression>"residuals"</s-expression> are allowed. If <s-expression>keep</s-expression> is <s-expression>TRUE</s-expression>, the complete set is saved.  
The default behavior is not to keep anything. 
</s-arg>

<s-arg name="fast">
if TRUE the robust initial estimate (used when fitting each of the reduced
models) is replaced by a weighted least squares estimate using the robust
weights stored in <s-expression>object</s-expression>.
</s-arg>
</s-args-optional>

<s-value>
An <s-expression>anova</s-expression> object is constructed, consisting of the term labels, the degrees  
of freedom, and Robust Final Prediction Errors (RFPE) for each subset model.  
If <s-expression>keep</s-expression> is missing, this is what is returned. If <s-expression>keep</s-expression> is present, a list  
with components <s-expression>"anova"</s-expression> and <s-expression>"keep"</s-expression> is returned. In this case, the  
<s-expression>"keep"</s-expression> component is a matrix of mode <s-expression>"list"</s-expression>, with a column for each  
subset model, and a row for each component kept. 
</s-value>

<s-details>
This function is a method for the generic function <s-expression>drop1</s-expression> for class  
<s-expression>"lmRob"</s-expression>. It can be invoked by calling <s-expression>drop1</s-expression> for an object of the  
appropriate class, or directly by calling <s-expression>drop1.lmRob</s-expression> regardless of  
the class of the object. 
</s-details>

<s-see>
<s-function name="add1.sgm">add1</s-function>,
<s-function name="anova.sgm">anova</s-function>,
<s-function name="drop1.sgm">drop1</s-function>,
<s-function name="lmRob.object.sgm">lmRob.object</s-function>.
</s-see>

<s-examples>
<s-example type = text>
stack.df &lt;- data.frame(Loss=stack.loss,stack.x) 
stack.rob &lt;- lmRob(Loss~Air.Flow+Water.Temp+Acid.Conc.,data=stack.df, 
                   robust.control=lmRob.robust.control(final="MM")) 
drop1(stack.rob) 
</s-example>
</s-examples>

<s-keywords>
<s-keyword>robust</s-keyword>
<s-keyword>regression</s-keyword>
<s-keyword>models</s-keyword>
<s-keyword>librobust</s-keyword>
</s-keywords>

<s-docclass>
function
</s-docclass>
</s-function-doc>
