Search results for "Segmented regression"
showing 8 items of 28 documents
Segmented relationships to model erosion of regression effect in Cox regression
2010
In this article we propose a parsimonious parameterisation to model the so-called erosion of the covariate effect in the Cox model, namely a covariate effect approaching to zero as the follow-up time increases. The proposed parameterisation is based on the segmented relationship where proper constraints are set to accomodate for the erosion. Relevant hypothesis testing is discussed. The approach is illustrated on two historical datasets in the survival analysis literature, and some simulation studies are presented to show how the proposed framework leads to a test for a global effect with good power as compared with alternative procedures. Finally, possible generalisations are also present…
A segmented regression model for event history data: an application to the fertility patterns in Italy
2009
We propose a segmented discrete-time model for the analysis of event history data in demographic research. Through a unified regression framework, the model provides estimates of the effects of explanatory variables and jointly accommodates flexibly non-proportional differences via segmented relationships. The main appeal relies on ready availability of parameters, changepoints, and slopes, which may provide meaningful and intuitive information on the topic. Furthermore, specific linear constraints on the slopes may also be set to investigate particular patterns. We investigate the intervals between cohabitation and first childbirth and from first to second childbirth using individual data …
Comment on "Estimating average annual per cent change in trend analysis"
2010
We discuss some issues relevant to paper of Clegg and co-authors published in Statistics in Medicine; 28, 3670-3682. Emphasis is on computation of the variance of the sum of products of two estimates, slopes and breakpoints.
The determination of maturity stages in male elasmobranchs (Chondrichthyes) using a segmented regression of clasper length on total length
2013
A novel statistical method for estimating the stages of maturity in male sharks and skates based on a segmented regression (SRM) is proposed. We hypothesize that this method is able to find the transition points in the three-phase relationship between total length (TL) and clasper length (CL). We applied an SRM to TL–CL data of nine species, from large pelagic sharks (e.g., Carcharhinus falciformis) to small coastal skates (e.g., Rioraja agassizi), captured in the southwestern Atlantic and northeastern Pacific. As expected, SRM detected two breakpoints, defining three maturity stages (immature, maturing, and mature), in six out of nine species. For three species, it was not possible to fin…
segmented: An R package to Fit Regression Models with Broken-Line Relationships
2008
Segmented or broken-line models are regression models where the relationships between the response and one or more explanatory variables are piecewise linear, namely represented by two or more straight lines connected at unknown values: these values are usually referred as breakpoints, changepoints or even joinpoints.
Determination of reflectance spectra model of skin phototypes V
2012
In dermatology, skin is assessed for its response to UV light and is categorised under the Fitzpatrick skin type (FST). The FST is commonly applied as a predictor of skin cancer. The FST classification however is subjective. To enable an objective assessment, a pattern model of skin colour taken from normal subjects is required. In this paper, a model for skin phototype (SPT) V is developed and presented. We conducted an observational study involving 41 participants with FST V. The study analysed the reflectance spectra of facultative skin and constitutive skin which was captured using spectrophotometer and multispectral camera. Using piecewise linear regression, we modelled the reflectance…
Smoothed score confidence interval for the breakpoint in segmented regression
2012
For the breakpoint parameter in segmented regression we consider confidence intervals based on the score statistic. Due to unsmoothness of the score, we propose to build the confidence intervals using its smoothed version under proper shape restrictions. Some simulations are presented to assess the finite sample performance of the proposed approach.
Testing for a breakpoint in segmented regression: a pseudo score approach
2011
To overcome the well known oddities in testing for the existence of a breakpoint in segmented regression models, we discuss a novel approach based on the Pearson X2 statistic which can be understood as an approximation of the Score statistic. We describe the method and present results from some simulations.