On optimal quantization rules for some problems in sequential decentralized detection

We consider the design of systems for sequential decentralized detection, a problem that entails several interdependent choices: the choice of a stopping rule (specifying the sample size), a global decision function (a choice between two competing hypotheses), and a set of quantization rules (the local decisions on the basis of which the global decision is made). This paper addresses an open problem of whether in the Bayesian formulation of sequential decentralized detection, optimal local decision functions can be found within the class of stationary rules. We develop an asymptotic approximation to the optimal cost of stationary quantization rules and exploit this approximation to show that stationary quantizers are not optimal in a broad class of settings. We also consider the class of blockwise stationary quantizers, and show that asymptotically optimal quantizers are likelihood-based threshold rules.Comment: Published as IEEE Transactions on Information Theory, Vol. 54(7), 3285-3295, 200

HopSkipJumpAttack: A Query-Efficient Decision-Based Attack

The goal of a decision-based adversarial attack on a trained model is to generate adversarial examples based solely on observing output labels returned by the targeted model. We develop HopSkipJumpAttack, a family of algorithms based on a novel estimate of the gradient direction using binary information at the decision boundary. The proposed family includes both untargeted and targeted attacks optimized for $\ell_2$ and $\ell_\infty$ similarity metrics respectively. Theoretical analysis is provided for the proposed algorithms and the gradient direction estimate. Experiments show HopSkipJumpAttack requires significantly fewer model queries than Boundary Attack. It also achieves competitive performance in attacking several widely-used defense mechanisms. (HopSkipJumpAttack was named Boundary Attack++ in a previous version of the preprint.

On surrogate loss functions and ff-divergences

The goal of binary classification is to estimate a discriminant function $\gamma$ from observations of covariate vectors and corresponding binary labels. We consider an elaboration of this problem in which the covariates are not available directly but are transformed by a dimensionality-reducing quantizer $Q$. We present conditions on loss functions such that empirical risk minimization yields Bayes consistency when both the discriminant function and the quantizer are estimated. These conditions are stated in terms of a general correspondence between loss functions and a class of functionals known as Ali-Silvey or $f$-divergence functionals. Whereas this correspondence was established by Blackwell [Proc. 2nd Berkeley Symp. Probab. Statist. 1 (1951) 93--102. Univ. California Press, Berkeley] for the 0--1 loss, we extend the correspondence to the broader class of surrogate loss functions that play a key role in the general theory of Bayes consistency for binary classification. Our result makes it possible to pick out the (strict) subset of surrogate loss functions that yield Bayes consistency for joint estimation of the discriminant function and the quantizer.Comment: Published in at http://dx.doi.org/10.1214/08-AOS595 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Trainee doctors' perceptions of the surgeon stereotype and its impact on professional identification: a qualitative study.

BACKGROUND The demography of the medical profession is changing as more women join the workforce. Traditional assumptions about the personal qualities required to be a successful surgeon may change as more women join the specialty. While exploring the attitudes and beliefs of doctors in their second 'Foundation' year of post-graduate training (FY2) about their choice of specialty, evidence emerged about how the stereotype of the surgeon influences professional identification and beliefs about person-specialty fit. METHODS Qualitative telephone interviews with 24 FY2 doctors, 17 women and 7 men, in South-West England. RESULTS Many participants reported exposure to stereotypes about the personal qualities desirable in a surgeon. Senior doctors and other trainees were the primary source of these stereotypical views. Experience on surgical placements could either reinforce stereotypes or challenge them, the latter particularly where senior surgeons provided positive role models. As more women enter the surgical specialties, they are increasingly challenging the traditional stereotype and sub-culture. CONCLUSION Gendered stereotypes about surgical roles persist, and for some this can hinder professional identification with the role. Positive role models and mentoring can encourage and support women who are interested a surgical career to identify with the role, but there is a need for a broader debate encompassing job redesign and surgical identities

What influences young doctors in their decision-making about general practice as a possible career? A qualitative study.

Background: Recruitment to General Practitioner (GP) training programmes in the United Kingdom is poor. Colleagues' negative comments about general practice could contribute to this.Aim: To investigate what influences Foundation Year 2 (FY2) doctors in their decisions to choose general practice as a career, and how colleagues' comments about GPs might affect those decisions.Design and Setting: A qualitative study in Southwest England.Method: Thematic analysis of interviews with FY2 doctors.Results: Twenty-four doctors participated. They thought that GPs worked hard and had very varied clinical work. The effect on their career choice depended on their personalities. GP placement experiences significantly influenced their career intentions. The loneliness of working in general practice was a key concern. FY2 doctors thought colleagues' criticisms of GPs did not reflect reality and were outdated. 'Banter' had little effect on career choices.Conclusion: Person-specialty fit and FY2 doctors' experiences of GP work have a significant effect on career choices. Loneliness in their GP work placements is a particular problem that should be addressed. While colleagues' derogatory comments about GPs may affect medical students' views on their career choices, they appear to have little effect on the career decision-making of qualified doctors.Abbreviations: CMT: Core Medical Training; FY2: Foundation Year 2; GP: general practitioner; NHS: National Health Service; UK: United Kingdom