1,247 research outputs found
White box radial basis function classifiers with component selection for clinical prediction models
Objective: To propose a new flexible and sparse classifier that results in interpretable decision support systems. Methods: Support vector machines (SVMs) for classification are very powerful methods to obtain classifiers for complex problems. Although the performance of these methods is consistently high and non-linearities and interactions between variables can be handled efficiently when using non-linear kernels such as the radial basis function (RBF) kernel, their use in domains where interpretability is an issue is hampered by their lack of transparency. Many feature selection algorithms have been developed to allow for some interpretation but the impact of the different input variables on the prediction still remains unclear. Alternative models using additive kernels are restricted to main effects, reducing their usefulness in many applications. This paper proposes a new approach to expand the RBF kernel into interpretable and visualizable components, including main and two-way interaction effects. In order to obtain a sparse model representation, an iterative l-regularized parametric model using the interpretable components as inputs is proposed. Results: Results on toy problems illustrate the ability of the method to select the correct contributions and an improved performance over standard RBF classifiers in the presence of irrelevant input variables. For a 10-dimensional x-or problem, an SVM using the standard RBF kernel obtains an area under the receiver operating characteristic curve (AUC) of 0.947, whereas the proposed method achieves an AUC of 0.997. The latter additionally identifies the relevant components. In a second 10-dimensional artificial problem, the underlying class probability follows a logistic regression model. An SVM with the RBF kernel results in an AUC of 0.975, as apposed to 0.994 for the presented method. The proposed method is applied to two benchmark datasets: the Pima Indian diabetes and the Wisconsin Breast Cancer dataset. The AUC is in both cases comparable to those of the standard method (0.826 versus 0.826 and 0.990 versus 0.996) and those reported in the literature. The selected components are consistent with different approaches reported in other work. However, this method is able to visualize the effect of each of the components, allowing for interpretation of the learned logic by experts in the application domain. Conclusions: This work proposes a new method to obtain flexible and sparse risk prediction models. The proposed method performs as well as a support vector machine using the standard RBF kernel, but has the additional advantage that the resulting model can be interpreted by experts in the application domain. © 2013 Elsevier B.V
The European Academy laparoscopic “Suturing Training and Testing’’ (SUTT) significantly improves surgeons’ performance
The efficiency of suturing training and testing (SUTT) model by laparoscopy was evaluated, measuring the
suturing skill acquisition of trainee gynecologists at the beginning and at the end of a teaching course. During a workshop organized by the European Academy of Gynecological Surgery (EAGS), 25 participants with three different experience levels in laparoscopy (minor, intermediate and major) performed the 4 exercises of the SUTT model (Ex 1: both hands stitching and continuous suturing, Ex 2: right hand stitching and intracorporeal knotting,
Ex 3: left hand stitching and intracorporeal knotting, Ex 4: dominant hand stitching, tissue approximation and
intracorporeal knotting). The time needed to perform the exercises is recorded for each trainee and group and statistical analysis used to note the differences. Overall, all trainees achieved significant improvement in suturing time (p < 0.005) as measured before and after completion of the training. Similar significantly improved suturing time differences (p < 0.005) were noted among the groups of trainees with different laparoscopic experience. In conclusion a short well-guided training course, using the SUTT model, improves significantly surgeon’s laparoscopic suturing ability, independently of the level of experience in laparoscopic surgery
Hipparcos red stars in the HpV_{T2} and VI_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibrated
instantaneous (epoch) Cousins color indices using newly derived
photometry. Three new sets of ground-based Cousins data have
been obtained for more than 170 carbon and red M giants. These datasets in
combination with the published sources of photometry served to obtain the
calibration curves linking Hipparcos/Tycho with the Cousins
index. In total, 321 carbon stars and 4464 M- and S-type stars have new
indices. The standard error of the mean is about 0.1 mag or better down
to although it deteriorates rapidly at fainter magnitudes. These
indices can be used to verify the published Hipparcos color
indices. Thus, we have identified a handful of new cases where, instead of the
real target, a random field star has been observed. A considerable fraction of
the DMSA/C and DMSA/V solutions for red stars appear not to be warranted. Most
likely such spurious solutions may originate from usage of a heavily biased
color in the astrometric processing.Comment: 10 figures, 1 electronic table, accepted in A&
Insights on the Role of Diabetes and Geographic Variation in Patients with Criticial Limb Ischaemia
AbstractBackgroundPatients with critical limb ischaemia (CLI) unsuitable for revascularisation have a high rate of amputation and mortality (30% and 25% at 1 year, respectively). Localised gene therapy using plasmid DNA encoding acidic fibroblast growth factor (NV1FGF, riferminogene pecaplasmid) has showed an increased amputation-free survival in a phase II trial. This article provides the rationale, design and baseline characteristics of CLI patients enrolled in the pivotal phase III trial (EFC6145/TAMARIS).MethodsAn international, double-blind, placebo-controlled, randomised study composed of 525 CLI patients recruited from 170 sites worldwide who were unsuitable for revascularisation and had non-healing skin lesions was carried out to evaluate the potential benefit of repeated intramuscular administration of NV1FGF. Randomisation was stratified by country and by diabetic status.ResultsThe mean age of the study cohort was 70 ± 10 years, and included 70% males and 53% diabetic patients. Fifty-four percent of the patients had previous lower-extremity revascularisation and 22% had previous minor amputation of the index leg. In 94% of the patients, the index leg had distal occlusive disease affecting arteries below the knee. Statins were prescribed for 54% of the patients, and anti-platelet drugs for 80%. Variation in region of origin resulted in only minor demographic imbalance. Similarly, while diabetic status was associated with a frequent history of coronary artery disease, it had little impact on limb haemodynamics and vascular lesions.ConclusionsClinical characteristics and vascular anatomy of CLI patients with ischaemic skin lesions who were unsuitable for revascularisation therapy show little variations by region of origin and diabetic status. The findings from this large CLI cohort will contribute to our understanding of this disease process.This study is registered with ClinicalTrials.gov, number NCT00566657
Outbursts of EX Hydrae Revisited
We present optical spectroscopy of EX Hya during its 1991 outburst. This
outburst is characterised by strong irradiation of the front face of the
secondary star by the white dwarf, an overflowing stream which is seen strongly
in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the
binary and spin phases. Strong irradiation of the accretion curtain and that of
the inner regions of the disc led to strong emission of HeII and to the
suppression of the Hg and Hb emission.
Disc overflow was observed in quiescence in earlier studies, where the
overflow stream material was modulated at high velocities close to 1000 km/s.
In outburst, the overflowing material is modulated at even higher velocities
(~1500 km/s). These are streaming velocities down the field lines close to the
white dwarf. Evidence for material collecting near the outer edge of the disc
and corotating with the accretion curtain was observed. In decline, this
material and the accretion curtain obscured almost all the emission near binary
phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse
minimum. This has provided additional evidence for an extended accretion
curtain, and for the corotation of material with the accretion curtain at the
outer edge of the disc. From these observations we suggest that a mechanism
similar to that of Spruit & Taam, where outbursts result due to the storage and
release of matter outside the magnetosphere, triggers the outbursts of EX Hya.
This is followed by the irradiation of the secondary star due to accretion
induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low
resolution. Paper accepted by the Monthly Notices of the Royal Astronomical
Societ
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