What is fractional polynomial?

What is fractional polynomial?

Fractional polynomials are an alternative to regular polynomials that provide flexible parameterization for continuous variables. For example, say we have an outcome y, a regressor x, and our research interest is in the effect of x on y.

How is the phreg procedure used in statistics?

The PHREG procedure performs regression analysis of survival data based on the Cox proportional hazards model. Cox’s semiparametric model is widely used in the analysis of survival data to explain the effect of explanatory variables on survival times. The survival time of each member of a population is assumed to follow its own hazard function,

How can I use fractional polynomials in SAS?

In SAS, this could be done with an ESTIMATE statement in PROC PHREG. But see also Sauerbrei et al., 2006: Multivariable regression model building by using fractional polynomials: Description of SAS, STATA and R programs which gives a macro for assessing fractional polynomial models in SAS, and also gives some examples of graphical visualisations.

How are fractional polynomials used in multivariable regression?

But see also Sauerbrei et al., 2006: Multivariable regression model building by using fractional polynomials: Description of SAS, STATA and R programs which gives a macro for assessing fractional polynomial models in SAS, and also gives some examples of graphical visualisations. [Footnote 3]

How are fractional polynomials used in regression models?

Fractional Polynomials. Fractional Polynomials are used in regression models to t non-linear functions. Often preferable to cut-points. Functions from fractional polynomials more exible than from ‘standard’ polynomials. See (Royston and Altman, 1994) or (Sauerbrei and Royston, 1999) for more details.

Can a quadratic be used as a fractional polynomial?

We could not have obtained that shape using a standard quadratic. Fractional polynomials provide a wide range of shapes that include all the shapes provided by ordinary polynomials and more. The fractional polynomial parameterization did not predetermine that the shape we obtained was skewed right.

Can a fractional polynomial produce a skewed right shape?

Fractional polynomials provide a wide range of shapes that include all the shapes provided by ordinary polynomials and more. The fractional polynomial parameterization did not predetermine that the shape we obtained was skewed right. Fractional polynomials can just as easily produce skewed left shapes.