# Questions tagged [fractional-polynomial]

Fractional polynomials is a method of fitting regression models using a set of fractional polynomial transformations of the independent variables. The set often includes -2, -1, -0.5, log, 0.5, 1, 2 and 3. Combinations (e.g. log x and x^(3/2)) are also possible.

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### Why adding $\log(x)$ for repeated powers in Fractional Polynomial Models?

I try to understand Fractional Polynomial Models like they are defined in Royston and Altman (1994). According to the paper, a Fractional Polynomial Model of degree 2 with a single covariate $X$ is ...
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### Polynomial Regression - Machine Learning

When I am working with polynomial regression in machine learning and as the degree of polynomial increases, what is the reason for increased data accuracy?
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### Multiple Regression Analysis Beginner

Background: I am using an instrument that measures two physical properties, X1~Temperture and X2~ Velocity. When gathering the data to make the curve a set of predetermined concentrations are chosen ...
750 views

### Interaction in fractional polynomial regression in R using the mfp package

I am modelling the relationship between waist circumference and triglycerides using fractional polynomials and the mfp package in R. I want to assess whether this relationship differs for ethnic ...
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### Type of regression for a mix dataset

I am building a model for the following TYPE of dataset: Target function has float numerical values Variables are: 2 variables are float values 4 other variables are integers (Yes/No = 1 or 0) ...
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### Approximation of fractional function that has real-power numerator

I have the function $f(x)=\frac{(1+x)^k}{1+ax}$, where $x>0, 0<a<k<1$. The function has only one maximum at $x_0=\frac{a-k}{a(k-1)}$, increases on the left of $x_0$ and decreases on the ...
317 views

### Partial residual plot not informative but transformations of predictor variables are required?

I have fitted a binary logistic regression model with two explanatory variables: $x_1,x_2$ using fractional polynomials (60k observations)(https://cran.r-project.org/web/packages/mfp/vignettes/...
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### How can missing data be dealt with when using splines or fractional polynomials?

I am reading Multivariable Model Building: A Pragmatic Approach to Regression Analysis Based on Fractional Polynomials for Modelling Continuous Variables by Patrick Royston and Willie Sauerbrei. So ...
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371 views

### Stability of univariate fractional polynomial models

I can't decide what is the best way to assess the stability of a higher order fractional polynomial model. To use an example I have been working on, I am analyzing a dataset with panel data selected ...
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769 views

### Significant turning points in fractional polynomials

When using fractional polynomial models it has been suggested to use the first derivative of the polynomial function to identify significant periods of change and the second derivative to identify ...
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### Fractional polynomials vs GAMs

I have been analyzing panel data for a while now using different methods (Generalized Linear Models, fractional polynomials and GAMs). If we just ignore GMMs for now, I have come to find that ...
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### Fractional polynomial model not converging in Stata

I am having trouble getting a fractional polynomial logistic model to converge using Stata 12. fracpoly, logistic: y x I have tried centering the dependent ...
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