Keyed Non-Parametric Hypothesis Tests

The recent popularity of machine learning calls for a deeper understanding of AI security. Amongst the numerous AI threats published so far, poisoning attacks currently attract considerable attention. In a poisoning attack the opponent partially tampers the dataset used for learning to mislead the classifier during the testing phase. This paper proposes a new protection strategy against poisoning attacks. The technique relies on a new primitive called keyed non-parametric hypothesis tests allowing to evaluate under adversarial conditions the training input's conformance with a previously learned distribution $\mathfrak{D}$. To do so we use a secret key $\kappa$ unknown to the opponent. Keyed non-parametric hypothesis tests differs from classical tests in that the secrecy of $\kappa$ prevents the opponent from misleading the keyed test into concluding that a (significantly) tampered dataset belongs to $\mathfrak{D}$.Comment: Paper published in NSS 201

Defacement Detection with Passive Adversaries

A novel approach to defacement detection is proposed in this paper, addressing explicitly the possible presence of a passive adversary. Defacement detection is an important security measure for Web Sites and Applications, aimed at avoiding unwanted modifications that would result in significant reputational damage. As in many other anomaly detection contexts, the algorithm used to identify possible defacements is obtained via an Adversarial Machine Learning process. We consider an exploratory setting, where the adversary can observe the detector’s alarm-generating behaviour, with the purpose of devising and injecting defacements that will pass undetected. It is then necessary to make to learning process unpredictable, so that the adversary will be unable to replicate it and predict the classifier’s behaviour. We achieve this goal by introducing a secret key—a key that our adversary does not know. The key will influence the learning process in a number of different ways, that are precisely defined in this paper. This includes the subset of examples and features that are actually used, the time of learning and testing, as well as the learning algorithm’s hyper-parameters. This learning methodology is successfully applied in this context, by using the system with both real and artificially modified Web sites. A year-long experimentation is also described, referred to the monitoring of the new Web Site of a major manufacturing company

A comparison of integrated testlet and constructed-response question formats

Constructed-response (CR) questions are a mainstay of introductory physics textbooks and exams. However, because of time, cost, and scoring reliability constraints associated with this format, CR questions are being increasingly replaced by multiple-choice (MC) questions in formal exams. The integrated testlet (IT) is a recently-developed question structure designed to provide a proxy of the pedagogical advantages of CR questions while procedurally functioning as set of MC questions. ITs utilize an answer-until-correct response format that provides immediate confirmatory or corrective feedback, and they thus allow not only for the granting of partial credit in cases of initially incorrect reasoning, but furthermore the ability to build cumulative question structures. Here, we report on a study that directly compares the functionality of ITs and CR questions in introductory physics exams. To do this, CR questions were converted to concept-equivalent ITs, and both sets of questions were deployed in midterm and final exams. We find that both question types provide adequate discrimination between stronger and weaker students, with CR questions discriminating slightly better than the ITs. Meanwhile, an analysis of inter-rater scoring of the CR questions raises serious concerns about the reliability of the granting of partial credit when this traditional assessment technique is used in a realistic (but non optimized) setting. Furthermore, we show evidence that partial credit is granted in a valid manner in the ITs. Thus, together with consideration of the vastly reduced costs of administering IT-based examinations compared to CR-based examinations, our findings indicate that ITs are viable replacements for CR questions in formal examinations where it is desirable to both assess concept integration and to reward partial knowledge, while efficiently scoring examinations.Comment: 14 pages, 3 figures, with appendix. Accepted for publication in PRST-PER (August 2014

The behavioural impact of a visually represented virtual assistant in a selfservice checkout context

Our research investigated whether the presence of an interface agent - or virtual assistant (VA) - in a self-service checkout context has behavioural effects on the transaction process during particular tasks. While many participants claimed to have not noticed a VA within the self-service interface, behaviour was still affected, i.e. fewer people made errors with the VA present than in the voice-only and control conditions. The results are explained as reflective of an unconscious observation of non-verbal cues exhibited by the VA. The results are discussed in relation to possible behavioural outcomes of VA presence.</p

Does personality influence web-based learning performance of novice programmers? A preliminary study

This paper presents a research investigating the effects of personality types and learning performance of student who learned introductory programming through content sequencing of web-based intstruction (WBI).A controlled laboratory experiment was conducted with the aim to understand whether personality types affect learning performance when students use the content sequencing system.Thirty eight first semester's students who enrolled in information technology (IT) program in a higher learning institution in Malaysia voluntarily participated in this study.Statistical analysis on the data from the experiment revealed interesting findings about the effect of personality on learning performance.This finding is discussed in relation to personality model for adaptive WBI

Determinants of IS continuance: the use of mobile computing services by field service staff in a South African mandatory setting

M.Com (Information Systems) by Research 8/31/2015 Research report submitted to the University of Witwatersrand in fulfilment of the requirements for the degree of Master of Commerce (Information Systems)Rugged mobile computing devices have enhanced durability and protection, thus allowing these devices to be used in the field as opposed to the office. These rugged mobile computing devices provide organisations with the ability to extend their information system services to their field staff, such as delivery persons, transport drivers and field technicians. Bhattacherjee's (2001) IS continuance model appears to fall short in explaining IS continuance in the context of field service staff who often perform repetitive tasks as part of their job as opposed to doing more complex tasks as performed by office bound knowledge workers. An IS continuance-based study in a South African organisation, where field service staff use rugged mobile devices, will improve our understanding of user behaviour towards technology within the body of IS knowledge. This study makes a contribution to theory by demonstrating that the core IS Continuance model by Bhattacherjee (2001), can be extended to include additional constructs to better predict IS continuance. This study proposes and tests an extension of Bhattacherjee’s (2001) IS continuance model, which explains the determinants of IS continuance intention in terms of affective and cognitive factors. The cognitive factors are task technology fit, perceived service availability, result demonstrability and the affective factor is the construct of familiarity. The study is carried out in a mandatory setting within the context of field technicians (working for a South African utility organisation) using application services on rugged mobile devices. To date, most IS continuance studies appear to have been carried out in a voluntary setting or an academic institution setting and very few of them have been conducted in organisations (mandatory settings). A structured questionnaire with closed questions was developed to capture field data from 144 participants on each of the study’s variables The hypotheses were tested using both parametric and non-parametric correlation and regression statistical analyses. The independent variables of perceived post-usage usefulness, familiarity and satisfaction explain approximately 51% of the variance in IS continuance intention. One of the key findings of the research is that perceived post usage usefulness loses its significance in the presence of Familiarity in predicting IS continuance intention. Thus, familiarity (affective factor) is the stronger predictor of IS continuance intention as opposed to the cognitive factors. In summary, this study showed that the affective factor is a stronger predictor of IS continuance intention than the cognitive factors, thus providing a richer understanding of IS continuance and a foundation for future research. Thus, in addition to methodological and contextual contributions, this study also contributes to theory

Nonparametric detection of signals causing arbitrary changes in the accompanying noise backgrounds

The detection of signals in the presence of noise is an important problem in the field of communications. The detection problem is concerned with the design of systems which determine only the presence or absence of a signal which occurs with background noise. An example of considerable importance, which is encountered quite frequently in practice, is the radar detection problem. In the radar problem it is desired to determine the presence of a target by detecting the presence of a radar return signal in noise. Another example is the seismic exploration problem which utilizes the detection of reflected signals from different depths of rock formations. In the past, most of the work in signal detection (1)-(5) has been limited to situations in which the signals were assumed to be of known deterministic form and the noise was assumed to be of known statistical form. This type of detection, which deals with signals and noise of known form, will be denoted as parametric detection (2). In some detection problems the information required by the detectors may be available. However, in other situations there may be much less information; for example, the statistical form of the noise may be unknown. In such cases, the parametric detectors become inappropriate. Thus, there is a need for a theory of detection systems which require much less a priori information than the parametric detectors. This detector, when the signal and noise are not completely known is called a nonparametric detector (2). The nonparametric detector originates from nonparametric statistical methods which are well covered in the literature (15)-(48). These nonparametric statistical methods (nonparametric detectors) have previously been applied to the problem of signal detection (6)-(14), but not nearly as extensively as the parametric detectors. These nonparametric detectors however, have been limited to the detection of signals which only change the dc level of the noise distribution when the signals are added to the noise. In this paper, nonparametric detectors will be considered, which not only will detect one specific class of signals, for example, signals which change the dc level of the noise distribution, but in general will detect signals which change the noise distribution in any respect. The signals will be assumed to be of the familiar additive variety (60). Using the goodness criterion of Asymptotic Relative Efficiency (A.R.E.) (9, 10, 14, 20), these nonparametric detectors are compared to the corresponding optimum parametric detectors, which are optimum in gaussian noise and gaussian signal plus noise. The A.R.E. of one detector with respect to another is an indication of how many more sample points on the observation interval one detector requires than the other to detect a weak signal with the same error levels. For a given noise distribution and a given signal plus noise distribution, the optimum detector is defined as that detector which requires the least number of sample points to achieve the desired accuracy. After the theory of these nonparametric detectors is developed, a nonparametric detector is used for the detection of a Frequency Modulated (FM) signal (49)-(59) in the presence of background noise under conditions of low(\u3c1) and extremely low (\u3c\u3c1) signal to noise ratios. Since many FM detection problems restrict attention to messages which are assumed to be expressed in a binary coded form (Binary Frequency Shift Keyed) or in r-ary coded form (Multiple Frequency Shift Keyed) (49)-(59), attention will be limited to FM signals of this form --Introduction, pages 1-3

Design of a sequential detector

The communication engineer has in the past treated the detection problem from a limited point of view. Detectors have been designed to reach a decision based on a specified number of samples. This approach has proved valuable, but it offers no provisions for an early decision if a conclusion becomes obvious early in the sampling. Neither is there an opportunity for additional sampling if necessary to reach a definite conclusion, because of these limitations it is desirable to find more general detectors. This study looks at a specific statistics (the sign test) and designs a sequential detector to utilize this statistic. The sequential detector is a type of detector where the decision to terminate depends only on the previous samples. This detector is also of the nonparametric class in that a complete knowledge of the signal and noise is not necessary for its operation --Abstract, page i

A Quantitative Analysis Of Leisure Participation Among Seafarers By Structural Equation Modelling

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2016Her denizci gemide çalışırken sosyal izolasyona maruz kalmaktadır. Denizciler karadan, ailelerinden, sevdiklerinden ve arkadaşlarından kontratları boyunca ayrı kalırlar. Gün geçtikçe azalan mürettebat sayısına karşın sorumluluklar, iş yükü ve evrak işleri sürekli artmaktadır. Bunun yanı sıra, gemi ortamında bir denizcinin arkadaşlık kurabileceği kişi sayısı da oldukça sınırlıdır ve bazen kişisel uyuşmazlıklardan dolayı hiç bir sosyal ilişkisi bile olmayabilir. Ayrıca, gemi ortamı denizciler için hem çalışma, hem dinlenme hem de yaşama ortamıdır. Bütün yaşamsal faaliyetlerini aynı kısıtlı ortamda gerçekleştirmek zorundadırlar. Kısacası, denizciliğin doğasında sosyal izolasyon mevcuttur. İnsan faktörü deniz kazalarına sebep olan ana unsur olarak görülmektedir. İnsan hatalarıda büyük bir oran ile sosyal izolasyondan ve onun insanlar üzerindeki etkilerinden kaynaklanmaktadır. Başka bir değiş ile, denizcilerin kontratları süresince sürekli mağruz kaldıkları sosyal izolasyon deniz kazalarına dolaylı olarak sebep olmaktadır. Duygular sosyal ve iletişimsel fonksiyonları içerir ve ayrıca insanların düşüncelerini ve niyetlerini birbirlerine iletir. Duyguların iyi bir düzeyde algılanması, düzenlenmesi ve kullanılması sosyal iletişimi arttırır ve sosyal izolasyonun etkisini azaltır. Ayrıca kişilerin yaşamlarından duydukları tatmin seviyeleri ile sosyal izolasyonun etkisi arasında negatif yönlü bir ilişki vardır. Yani, yaşam tatminleri ve duygusal zekaları yüksek kişiler sosyal izolasyonun etkisini daha az hissederler. Bununla birlikte, serbest zaman aktivitelerinin duygusal zekayı arttırdığı, yaşam tatminini yükselttiği ve sosyal etkileşimi güçlendirdiği bilinmektedir. Buna ek olarak, Uluslararası Çalışma Örgütü Denizcilik Çalışma Sözleşmesinde (MLC, 2006) serbest zamana yönelik rekreasyonel imkanların gemide ve sahil tehsislerinde sağlanmasının önemini vurgulamaktadır. Bu bağlamda sosyal izolasyona maruz kalan denizcileri, serbest zaman aktivitelerine yönlendirerek, onların sosyal iletişimlerinin ve duygusal zekalarının artması ve yaşam tatminlerinin yükselmesi ile sosyal izolasyonun ve deniz kazalarında insan faktörünün etkisinin azalabileceği ön görülüp, bu kavramlar arasındaki ilişkiler incelenmiştir. Serbest zaman katılımcısı olan denizcilerin ciddi ve kayıtsız olmak üzere iki gruba ayrılıp ayrılamadığı incelenmiştir. Daha sonra ciddi ve kayıtsız serbest zaman katılımcılarının tipolojilerini çıkarmak için, bu iki grup kendi aralarında demografik özelliklerine, serbest zaman tatmin düzeylerine, yaşam tatmin düzeylerine ve duygusal zekalarına göre kıyaslanmıştır. Ayrıca, denizciler arasında serbest zaman katılımı, serbest zaman tatmini, yaşam tatmini ve duygusal zeka düzeyleri arasındaki ilişkilerin incelenmesi için Yapısal Eşitlik Modellemesi (YEM) kurulmuştur. Araştırmanın çalışma gurubu farklı yeterlilik düzeyindeki, 23’ü kadın, 194’ü erkek olamak üzere 217 Türk denizciden oluşmaktadır. Bütün istatistiksel analizler IBM SPSS Statistics 23, IBM SPSS Amos 23 ve Rstudio’nun en son sürümü kullanılarak gerçekleştirilmiştir. İlk olarak, örnekleme ve çalışmanın amacına uygun ölçeklerin seçilmesi için literatür taraması yapılmış ve en uygun ölçekler belirlenmiştir. Sonrasında, seçilmiş olan “Ciddi ve Kayıtsız Serbest Zaman Ölçeği (CKSZ)”, “Serbest Zaman Tatmin Ölçeği”, “Yaşam Tatmin Ölçeği” ve “Duygusal Zeka Ölçeği” nin ölçme modellerinin doğrulanması amaçlanmıştır. Bu bağlamda, kayıp değerler, uç değerler, çoklu doğrusallık, tekillik ve normallik testleri yapılmış, güvenirlilik ve doğrulayıcı faktör analizi sonuçları incelenmiştir. Kayıp değer oranının %3 den az olması sebebiyle serilerin ortalamaları yöntemi ile kayıp değerlere yeni değerler atanmıştır. Uç değerlerin sonucu saptıracağı ve örneklem dışı olabilecekleri düşünüldüğünden bu değerler veri setinden çıkartılmıştır. Yapılan analizler sonucunda bütün değişkenler arasında çoklu doğrusallık ve tekillik sorunu bulunmamıştır. Ayrıca parametrik testlerin en önemli önşartlarından biri olan normal dağılım varsayımının sağlanması için kesikli verilerde kullanılan veri iyileştirme/dönüştürme yöntemleri araştırılmış ve veri setine en uygun olan dönüşüm metodu uygulanmıştır. Son olarak herbir ölçeğin alt faktörleri ile birlikte kabul edilir düzeyde iç tutarlılık katsayısına sahip oldukları ve faktör yapılarının bu çalışmanın örneklemi için doğrulandığı görülmüştür. Bu testler sonucunda bütün ölçeklerin ileriki aşamalarda parametrik testlerin uygulanması için kabul edilebilir anlamlılık düzeyinde olduğu gözlemlenmiştir. Daha sonra, CKSZ ölçeğinin faktörlerine göre serbest zaman katılımcılarının kaç kümeye ayrıldığının testi için Rstudio istatistik programında NbClust paketi kullanılmıştır. Kesikli veriler için en uygun uzaklık ölçümü olan öklid uzaklığı kullanılmış, Ward ve K-means metotları ile en uygun küme sayısı belirlenmeye çalışılmıştır. Analiz sonucunda, bu ölçeğin dokuz faktörlü yapısı ışığında en uygun küme sayısının 2 olduğu belirlenmiştir. Küme sayısı belirlendikten sonra, serbest zaman katılımcılarını ait oldukları kümelere yerleştirmek için Fuzzy C-Means (FCM) algoritması kullanılmıştır. Bu algoritma Rstudio’da “e1071” paketinindeki “cmeans” komutu ile çalıştırılmıştır. FCM analizi sonucunda, 108 serbest zaman katılımcısı ciddi serbest zaman katılımı grubuna, 109 serbest zaman katılımcısı da kayıtsız serbest zaman katılımı grubuna yerleştirilmiştir. Kümelerin faktörler bazında ortalamaları incelendiğinde, ciddi katılımcıların ortalamalarının, kayıtsız katılımcılardan yüksek olduğu gözlemlenerek, kümeleme analizi doğrulanmıştır. Kümeleme analizinden sonra, CKSZ’nin hangi faktörünün daha iyi ayırma yüküne sahip olduğunu ve faktörler arası önem sıralarını belirlemek için ayırma (dikriminant) analizi uygulanmıştır. Kovaryans matrislerinin eşitliği “Box-M” testi ile test edilmiş ve p.05). Öte yandan, serbest zaman tatminlerine, yaşam tatminlerine ve duygusal zekalarına göre anlamlı düzeyde farklılık gösterdikleri tespit edilmiştir (pSocial isolation of the seafarers - which induces human factor in marine accidents - is an important problem driver in the ship environment. Seafarers are being away from land, their family, their friends for many months and accordingly they are inherently isolated from social world while they are serving on-board. On the other hand, emotional competencies and subjective well-being are able to break social isolation. Also, it is suggested by some researchers that ordinary participation in leisure activities can enhance individual emotional development, provide physical and mental health as well as an improved social interaction and produce satisfaction with life. Furthermore, Maritime Labour Convention, 2006 (MLC, 2006) adopted by the International Labour Organization (ILO) points out the significance of providing the recreational facilities both on-board and on-shore. In this context, the aim of this study is to classify participants into two group as serious leisure (SL) or casual leisure (CL), and to compare serious and casual leisure groups each other based on demographic specifications, leisure satisfaction, satisfactions with life and emotional abilities. Besides, this research intends to find out whether there are any relationships between leisure participation, leisure satisfaction, life satisfaction and emotional intelligence among seafarers by Structural Equation Modelling (SEM). Thus a survey has been conducted among 217 seafarers by means of a questionnaire including "Serious and Casual Leisure Measure (SCLM)", "Leisure Satisfaction Scale (LSS)", "Shcutte Emotional Intelligence Scale (SEIS)" and "Satisfaction with Life Scale (SWLS)", and the results have been evaluated. All calculations have been performed by using IBM SPSS Statistics 23, IBM SPSS Amos 23 and latest version of Rstudio. Fuzzy C-Means cluster analysis is conducted to classify leisure participants by factors of SCLM. After classifying participants as serious or casual, discriminant analysis is applied to evaluate importance level of each factors and to identify which factors make better distinction between clusters. Next, in order to demonstrate the profile of clusters differences between serious and casual groups are identified by crosstabs including demographics, frequency of doing leisure activities, leisure satisfaction, life satisfaction and emotional intelligence and chi-square analysis is utilized to recognize whether results are statistically significant. Finally, Structural Equation Model (SEM) is used to find out the relationship between leisure participation, leisure satisfaction, life satisfaction and emotional intelligence among seafarers. test first conceptual model of research established to break social isolation of seafarers. It is aimed to examine regression and path coefficients between latent factors and observed variables in accordance with established conceptual model. As a result of all findings, seafarers can be divided into two groups as serious and casual have more leisure satisfaction, more emotional intelligent and more satisfaction with their lives than casual ones. Furthermore, there are positive relationship between leisure participation, leisure satisfaction, life satisfaction and emotional intelligence among seafarers. Consequently, providing leisure facilities both on-board and onshore for seafarers, and supporting and encouraging them to join leisure activates as a serious participant can break social isolation by enhancing the emotional intelligence and life satisfaction. Therefore, specific training programs for encouraging seafarers to participate recreational and leisure activities could be conducted by authorities.Yüksek LisansM.Sc

ArraySolver: An Algorithm for Colour-Coded Graphical Display and Wilcoxon Signed-Rank Statistics for Comparing Microarray Gene Expression Data

The massive surge in the production of microarray data poses a great challenge for proper analysis and interpretation. In recent years numerous computational tools have been developed to extract meaningful interpretation of microarray gene expression data. However, a convenient tool for two-groups comparison of microarray data is still lacking and users have to rely on commercial statistical packages that might be costly and require special skills, in addition to extra time and effort for transferring data from one platform to other. Various statistical methods, including the t-test, analysis of variance, Pearson test and Mann–Whitney U test, have been reported for comparing microarray data, whereas the utilization of the Wilcoxon signed-rank test, which is an appropriate test for two-groups comparison of gene expression data, has largely been neglected in microarray studies. The aim of this investigation was to build an integrated tool, ArraySolver, for colour-coded graphical display and comparison of gene expression data using the Wilcoxon signed-rank test. The results of software validation showed similar outputs with ArraySolver and SPSS for large datasets. Whereas the former program appeared to be more accurate for 25 or fewer pairs (n ≤ 25), suggesting its potential application in analysing molecular signatures that usually contain small numbers of genes. The main advantages of ArraySolver are easy data selection, convenient report format, accurate statistics and the familiar Excel platform