Encrypted statistical machine learning: new privacy preserving methods

We present two new statistical machine learning methods designed to learn on fully homomorphic encrypted (FHE) data. The introduction of FHE schemes following Gentry (2009) opens up the prospect of privacy preserving statistical machine learning analysis and modelling of encrypted data without compromising security constraints. We propose tailored algorithms for applying extremely random forests, involving a new cryptographic stochastic fraction estimator, and na\"{i}ve Bayes, involving a semi-parametric model for the class decision boundary, and show how they can be used to learn and predict from encrypted data. We demonstrate that these techniques perform competitively on a variety of classification data sets and provide detailed information about the computational practicalities of these and other FHE methods.Comment: 39 page

Top executive compensation in less developed capital markets

Purpose – This paper aims to study the determinants of variable compensation for top Portuguese executives (chief executive officers, chief financial officers and commercial directors). Design/methodology/approach – Data from 101 firms were collected through an email questionnaire sent to the human resource directors of 500 largest and best Portuguese firms of Exame, a business newspaper. A Tobit regression analysis was used to estimate the basic equation of the study. Findings – The conclusions are generally consistent with findings obtained in more developed capital markets. It was found that public and older corporations are more intensive users of variable pay, consistent with the agency theory prediction. A location in the centre of economic activity and a higher executive education increase the propensity to receive higher levels of salary in the form of variable compensation. The relation between compensation and performance was more elusive. Research limitations/implications – There are limitations as to the extrapolation of the obtained results, as the level of potential idiosyncrasy cannot be measured. Ideally, the study should be replicated in different contexts to control for country-specific influences. Nevertheless, the main finding that performance-related pay mechanisms are less used in countries where public corporations and potential agency problems are less pervasive should hold. Originality/value – As the focus is on a small economy with a developing capital market, this paper contributes to executive compensation literature that has mostly analysed firms based in well-developed capital markets, with a higher separation of ownership and control (Anglo-Saxon countries).info:eu-repo/semantics/submittedVersio

Classe de Ciências

info:eu-repo/semantics/publishedVersio

Modelos de crescimento e governação das transacções no sector das embalagens: três casos portugueses

No sector português das embalagens identificámos três casos de modelos estratégicos distintos de crescimento e governação das transacções. Apesar do longo debate sobre onde desenhar as fronteiras da empresa, persiste a ausência de consenso, e diferentes teorias propõem diversas soluções. Este estudo contribui para o debate com o estudo de três casos portugueses. Os modelos estratégicos adoptados pelas três empresas são profundamente diferentes, mas viabilizam elevado desempenho e expansão comercial. Uma empresa assume um modelo clássico de centralização da produção e de serviço dos clientes através de relações de mercado quase puras. Outra empresa, um modelo de elevada integração vertical que corresponde à externalização integral das actividades produtivas dos clientes. A terceira, um modelo especializado de integração com a estrutura produtiva dos clientes, a um nível de quase integração vertical, com a instalação wall to wall de pequenas a médias fábricas. Os três casos parecem evidenciar que o estabelecimento de parcerias e o nível de confiança estabelecido, foram decisivos para a sobrevivência e expansão das empresas.info:eu-repo/semantics/publishedVersio

Quo vadis microcredit in Portugal? A case study of the day-to-day of an entrepreneur

A literature survey shows conflicts among the expected advantages of microcredit public-policies that might lead to discomfort on decision-making, and self-protection reactions due to increasing social demand for accountability. So, decisionmakers lacking skills and sensitiveness to the entrepreneurial phenomenon, set assessment criteria, based on banking practice, inadequate to unemployed, young, low income entrepreneurs. Together with unorganized processes, this situation produces disrespectful loan proposals ignoring experts’ opinions and business plans/contexts. The exploratory case of a Mutual Guarantee Society guaranteed by public funding: exemplifies ridiculous loan proposals for microcredit funding, conflicting with social grounds; shows entrepreneurs difficulties in accessing microcredit public-policies.info:eu-repo/semantics/acceptedVersio

Determinantes da remuneração nas empresas portuguesas

A análise e explicação das determinantes das diversas formas de remuneração em Portugal são o principal objectivo deste trabalho. Apesar da existência de diversos estudos sobre remunerações, até agora não foram desenvolvidos estudos sobre quais as determinantes explicativas da realidade empresarial. Este estudo identifica o conjunto de características das empresas e dos colaboradores que explicam o montante e a probabilidade de auferir remuneração variável e quais as determinantes da remuneração base, comparando-se os dois modelos através do «colaborador padrão». Os resultados mostram que a remuneração variável é mais utilizada nos níveis hierárquicos superiores, na área comercial, em empresas de menor dimensão, em filiais de empresas estrangeiras e para colaboradores com educação superior. Quanto à rendibilidade, os resultados revelam uma relação positiva com a probabilidade de existência de remuneração variável. No entanto, os montantes de remuneração variável são mais elevados nas empresas com menor rendibilidade

What drives foreign direct investment: the role of language, geographical distance, information flows and technological similarity

This paper sheds new light on the impact of linguistic and technological similarities between countries on foreign direct investment (FDI), using an extended gravity model. The model includes technological commonality, as measured by the aggregate production of intellectual property, at the country level. An analysis of 71,309 pairs of FDI relationships, from 2000 to 2012, showed that language is positively associated with a high level of FDI. Technological differences do impede the flow of FDI between countries, and information flow is crucial for large flows of FDI. Information flow diminishes the negative impact of distance.info:eu-repo/semantics/acceptedVersio

Encrypted accelerated least squares regression.

Information that is stored in an encrypted format is, by definition, usually not amenable to statistical analysis or machine learning methods. In this paper we present detailed analysis of coordinate and accelerated gradient descent algorithms which are capable of fitting least squares and penalised ridge regression models, using data encrypted under a fully homomorphic encryption scheme. Gradient descent is shown to dominate in terms of encrypted computational speed, and theoretical results are proven to give parameter bounds which ensure correctness of decryption. The characteristics of encrypted computation are empirically shown to favour a non-standard acceleration technique. This demonstrates the possibility of approximating conventional statistical regression methods using encrypted data without compromising privacy

Why discouraged borrowers exist? An empirical (re)examination from less developed countries

Using the fourth-round database of the Business Environment and Enterprise Performance Survey (2008/09 BEEPS), this study examines the determinants of discouragement in less developed countries in Eastern Europe and Central Asia. The results show that whereas firms' opaqueness, demographic factors, and distance between lenders and borrowers better explain the discouragement due to tough loan prices and/or loan application procedures, firm risk and banking concentration explain the incidence of discouraged borrowers due to the fear of rationing. Innovator status, the legal protection of creditors and lenders in the event of default, and the coverage of information sharing instruments help explain discouragement in a transversal way.info:eu-repo/semantics/acceptedVersio