İstatistik Bilim Dalı Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/4382
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Article Assessment of the Use of AutoCAD in Mechanical Engineering Technical Drawing Education(2017) Akyürek, Turgut: AutoCAD is one of the widely used software tools in engineering education. In this study, a general assessment of AutoCAD for the usage in the mechanical engineering technical drawing education is made. AutoCAD is assessed in terms of the fulfilment of the requirements defined for the main two technical drawing courses. AutoCAD is assessed in terms of its capability in meeting the requirements of the technical drawing coursesArticle Normal Olmayan Dağılımlar Altında Tahminin Basit Doğrusal Profil İzleme Üzerine Etkisi(2019) Bayrak, Özlem Türker; Aytaçoğlu, BurcuSon yıllarda, bir ürün veya sürecin kalitesinin tepki ve açıklayıcı değişken(ler) arasındaki ilişkinin fonksiyonu ile ifade edildiği profillerin izlenmesi için pek çok kalite şeması önerilmiştir. Bu yöntemlerin çoğu Faz II analizlerinde kontrol parametre değerlerinin bilindiğini ve artıkların normal dağıldığını varsaymaktadır. Oysaki uygulamada parametreler Faz I analizlerinde tahmin edilir ve artıklar normal olmayabilir. Bu çalışmada simülasyon ile artıkların t dağıldığı ve parametrelerin tahmin edildiği durumlarda basit doğrusal profillerin izlenmesi için önerilen T2, EWMA-R ve EWMA-3 yöntemlerinin performansları değerlendirilmiştir. Performans ölçüsü olarak hem ortalama koşu uzunluğu hem de koşu uzunluğu standart sapması dikkate alınmıştır. En sonunda uygulayıcılar için bazı öneriler tablo halinde özetlenmiştir.Article Doğrusal Profillere Dayalı Kontrol Şemalarının Ekonomide Erken Uyarı Sistemi Oluşturmak İçin Uyarlanması: Enerji Sektöründe Bir Pilot Çalışma(2019) Haliloğlu, Ebru Yüksel; Bayrak, Özlem Türker; Aytaçoğlu, BurcuBu çalışmada, küresel krizleri öngörebilmek ve dolayısıyla karar alıcılar tarafından önleyici aksiyonlar alınabilmesi amacıyla erken uyarı sistemi oluşturmak üzere doğrusal profil için kontrol şemaları adapte edilmiştir. Bu doğrultuda, gayri safi yurt içi hasıla (GSYH) ile G8 ve gelişmekte olan büyük ülkelerin 1980-2012 yıllarındaki enerji tüketimi arasındaki ilişki incelenmiştir. Faz I analizi model parametrelerinin zaman içinde otokorelasyon içerdiğini göstermiştir. Dolayısıyla, bu otokorelasyonu dikkate alan, doğrusal profiller için Shewhart ve EWMA şemaları kullanılmış ve EWMA şemasının daha iyi olduğu tespit edilmiştir. 2008 küresel krizinin tespit edilebildiği ancak yerel Asya krizinin tespit edilemediği görülmüştür. Bu çalışma, hem doğrusal profillerin izlenmesi için geliştirilen kontrol şemalarını erken uyarı sistemi oluşturmak amacıyla kullanan hem de açıklayıcı değişkenlerin (x-değerleri) profilden profile çeşitlilik arz etmesi ile profiller arası korelasyonu da dikkate alan ilk çalışmadır.Article Citation - Scopus: 1Linear Contrasts in One-Way Classification Ar(1) Model With Gamma Innovations(Hacettepe Univ, Fac Sci, 2016) Senoglu, Birdal; Bayrak, Ozlem TurkerIn this study, the explicit estimators of the model parameters in oneway classification AR(1) model with gamma innovations are derived by using modified maximum likelihood (MML) methodology. We also propose a new test statistic for testing linear contrasts. Monte Carlo simulation results show that the MML estimators have higher efficiencies than the traditional least squares (LS) estimators and the proposed test has much better power and robustness properties than the normal theory test.Article Citation - WoS: 1Citation - Scopus: 2Sample Design and Allocation for Random Digit Dialling(Springer, 2005) Ayhan, HO; Islam, MQSample design and sample allocation methods are developed for random digit dialling in household telephone surveys. The proposed method is based on a two-way stratification of telephone numbers. A weighted probability proportional to size sample allocation technique is used, with auxiliary variables about the telephone coverage rates, within local telephone exchanges of each substrata. This makes the sampling design nearly "self-weighting" in residential numbers when the prior information is well assigned. A computer program generates random numbers for the local areas within the existing phone capacities. A simulation study has shown greater sample allocation gain by the weighted probabilities proportional to size measures over other sample allocation methods. The amount of dialling required to obtain the sample is less than for proportional allocation. A decrease is also observed on the gain in sample allocation for some methods through the increasing sample sizes.Article Citation - Scopus: 1Inference of Autoregressive Model With Stochastic Exogenous Variable Under Short-Tailed Symmetric Distributions(Springer international Publishing Ag, 2018) Bayrak, Ozlem Tuker; Akkaya, Aysen DenerIn classical autoregressive models, it is assumed that the disturbances are normally distributed and the exogenous variable is non-stochastic. However, in practice, short-tailed symmetric disturbances occur frequently and exogenous variable is actually stochastic. In this paper, estimation of the parameters in autoregressive models with stochastic exogenous variable and non-normal disturbances both having short-tailed symmetric distribution is considered. This is the first study in this area as known to the authors. In this situation, maximum likelihood estimation technique is problematic and requires numerical solution which may have convergence problems and can cause bias. Besides, statistical properties of the estimators can not be obtained due to non-explicit functions. It is also known that least squares estimation technique yields neither efficient nor robust estimators. Therefore, modified maximum likelihood estimation technique is utilized in this study. It is shown that the estimators are highly efficient, robust to plausible alternatives having different forms of symmetric short-tailedness in the sample and explicit functions of data overcoming the necessity of numerical solution. A real life application is also given.Article Citation - WoS: 1Citation - Scopus: 1Effect of Estimation Under Nonnormality on the Phase Ii Performance of Linear Profile Monitoring Approaches(Wiley, 2019) Aytacoglu, Burcu; Bayrak, Ozlem Turker; Türker Bayrak, ÖzlemThe number of studies about control charts proposed to monitor profiles, where the quality of a process/product is expressed as function of response and explanatory variable(s), has been increasing in recent years. However, most authors assume that the in-control parameter values are known in phase II analysis and the error terms are normally distributed. These assumptions are rarely satisfied in practice. In this study, the performance of EWMA-R, EWMA-3, and EWMA-3(d(2)) methods for monitoring simple linear profiles is examined via simulation where the in-control parameters are estimated and innovations have a Student's t distribution or gamma distribution. Instead of the average run length (ARL) and the standard deviation of run length, we used average and standard deviation of the ARL as performance measures in order to capture the sampling variation among different practitioners. It is seen that the estimation effect becomes more severe when the number of phase I profiles used in estimation decreases, as expected, and as the distribution deviates from normality to a greater extent. Besides, although the average ARL values get closer to the desired values as the amount of phase I data increases, their standard deviations remain far away from the acceptable level indicating a high practitioner-to-practitioner variability.