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help for ^stselpre^                                            [ec]  Feb 10, 2010
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Fits proportional hazards model to case-cohort data
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    ^stselpre^ varlist [^if^ exp] [^in^ range] [^, nohr^ ^l^evel^(^#^)^ ^self^
               {^bre^slow | ^efr^on | ^exactm^ | ^exactp^} ^nosh^ow  ^force^ ]


^stselpre^ is for use with survival-time data; see help @st@. Before using the command,
data must be prepared for case-cohort analysis by ^stcascoh^; see help @stcascoh@.


Description
-----------

^stselpre^ returns estimates and standard errors from proportional hazards fit to
case-cohort data. Coefficients are estimated according to two methods:

- Self-Prentice scheme. Risk sets uses just the sub-cohort member at risk,
- Prentice scheme. Risk sets are augmented by non sub-cohort cases when they fail.

The asymptotic Self-Prentice method variance-covariance matrix and standard errors are
computed using the simplification  described in Therneau and Li (1999).

The syntax of @predict@ following ^stselpre^ is as in ^stcox^


Options
-------

^nohr^ specifies that coefficients rather than hazard ratios are to be displayed 
    ^nohr^ may be typed at estimation or when replaying previously estimated results.

^level(^#^)^ specifies the confidence level for the confidence intervals of the
    coefficients; see help @level@. ^level^ may be also specified when replaying previously
    estimated results.

^self^ specifies that Self-Prentice method coefficient vector is to be saved in e(b).
    Prentice method coefficients are saved by default. 

^breslow^, ^efron^, ^exactm^, and ^exactp^ each specify a method for handling tied
    deaths that the underlying ^stcox^ command executes. ^efron^ is the default.

^noshow^ prevents ^stselpre^ from displaying the identities of the key st variables
    above its output.

^force^ prevents ^stselpre^ from doing some check on the data set previously prepared by ^stcascoh^.



Examples
--------

        . ^stselpre stage age^
        . ^xi: stselpre i.stage*i.histol, nohr self^


Also see
--------

 Manual:  ^[R] stcox  [R] sttocc^
On-line:  help for @stcascoh@  @stcox@  @sttocc@



Reference
---------

Therneau M T, Li H: Computing the Cox Model for Case Cohort Designs.
           Lifetime Data Analysis 1999; 5: 99-112.


Author
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      Enzo Coviello
      Epidemiology Unit ASL BT 
      Italy
      enzo.coviello@@alice.it
