Key points are not available for this paper at this time.
Patrick Royston, Douglas G. Altman, Regression Using Fractional Polynomials of Continuous Covariates: Parsimonious Parametric Modelling, Journal of the Royal Statistical Society. Series C (Applied Statistics), Vol. 43, No. 3 (1994), pp. 429-467
Royston et al. (Sat,) studied this question.