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

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