430 research outputs found
Study of international experience regarding issues of access to higher education: the US case
Μελέτη της διεθνούς εμπειρίας αναφορικά με το ζήτημα της πρόσβασης στην τριτοβάθμια εκπαίδευσ
Statistical Optimality of Stochastic Gradient Descent on Hard Learning Problems through Multiple Passes
We consider stochastic gradient descent (SGD) for least-squares regression
with potentially several passes over the data. While several passes have been
widely reported to perform practically better in terms of predictive
performance on unseen data, the existing theoretical analysis of SGD suggests
that a single pass is statistically optimal. While this is true for
low-dimensional easy problems, we show that for hard problems, multiple passes
lead to statistically optimal predictions while single pass does not; we also
show that in these hard models, the optimal number of passes over the data
increases with sample size. In order to define the notion of hardness and show
that our predictive performances are optimal, we consider potentially
infinite-dimensional models and notions typically associated to kernel methods,
namely, the decay of eigenvalues of the covariance matrix of the features and
the complexity of the optimal predictor as measured through the covariance
matrix. We illustrate our results on synthetic experiments with non-linear
kernel methods and on a classical benchmark with a linear model
Exponential convergence of testing error for stochastic gradient methods
We consider binary classification problems with positive definite kernels and
square loss, and study the convergence rates of stochastic gradient methods. We
show that while the excess testing loss (squared loss) converges slowly to zero
as the number of observations (and thus iterations) goes to infinity, the
testing error (classification error) converges exponentially fast if low-noise
conditions are assumed
Primary reverse total shoulder arthroplasty in patients older than 80 years: clinical and radiologic outcome measures
BACKGROUND
The use of reverse total shoulder arthroplasty (RTSA) has spread worldwide as a result of an expansion of indications and an aging society. However, the value of RTSA for very old patients is rarely analyzed. This study was conducted to investigate the outcome of primary RTSA in patients older than 80 years.
METHODS
We identified 171 shoulders (159 patients) treated with RTSA at an age of more than 80 years between January 2005 and March 2018. The primary outcome parameters were Subjective Shoulder Value (SSV) and the Constant-Murley score, mortality, complications, and reoperation rates. Secondary outcomes were adverse radiographic outcomes. A minimum follow-up of 1 year was accepted in 14 patients (8%) because of these patients' older age.
RESULTS
We included 171 cases (159 patients; 120 female) with a mean age of 84 ± 3 years (range 80.1-94). The main indication for RTSA was cuff tear arthropathy (43%), isolated rotator cuff tear (22%), and fracture (21%). A total of 136 patients (79%) were eligible for physical examination with a mean follow-up of 41 ± 25 months (12-121). Relative Constant-Murley scores improved significantly from 39% ± 19% to 77% ± 16% and SSV from 31% ± 18% to 74% ± 22%. The range of motion and force improved significantly as well. The surgical site complication rate was 30%, with a reoperation rate of 8% (13 patients) mainly due to fracture and glenoid loosening. The overall mortality was 16% with a mean time to death of 53 ± 31 months (95% confidence interval 15, 120), thereby no higher than the age-adjusted, expected mortality rate without this procedure.
CONCLUSION
Despite a quite high postoperative complication rate, RTSA is a valid therapeutic option in patients older than 80 years, with an unexpectedly low medical complication rate and good to excellent improvement of shoulder function and pain
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Sentence repetition in adolescents with specific language impairments and autism: an investigation of complex syntax
Background: Recent studies have indicated that many children with autism spectrum disorders present with language difficulties that are similar to those of children with specific language impairments, leading some to argue for similar structural deficits in these two disorders.
Aims: Repetition of sentences involving long-distance dependencies was used to investigate complex syntax in these groups.
Methods & Procedures: Adolescents with specific language impairments (mean age = 15;3, n = 14) and autism spectrum disorders plus language impairment (autism plus language impairment; mean age = 14;8, n = 16) were recruited alongside typically developing adolescents (mean age = 14;4, n = 17). They were required to repeat sentences containing relative clauses that varied in syntactic complexity.
Outcomes & Results: The adolescents with specific language impairments presented with greater syntactic difficulties than the adolescents with autism plus language impairment, as manifested by higher error rates on the more complex object relative clauses, and a greater tendency to make syntactic changes during repetition.
Conclusions & Implications: Adolescents with specific language impairments may have more severe syntactic difficulties than adolescents with autism plus language impairment, possibly due to their short-term memory limitations
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