Article citation info:Type-2 fuzzy sets were initially given by Zadeh as an extension of type-1 fuzzy sets. There is a growing interest in type-2 fuzzy set and its memberships (named secondary memberships) to handle the uncertainty in type-1 fuzzy set and its primary membership values. However, arithmetical operators on type-2 fuzzy sets have computational complexity due to third dimension of these sets. In this study, we present some mathematical operators which can be easily applied to type-2 fuzzy sets and numbers. Also, mathematical functions of type-2 fuzzy numbers are given according to their monotonicity. These functions are adapted to reliability and distribution functions of the random variables with the type-2 fuzzy parameters. These functions are applied to Exponential, Chi-square, Weibull distributions with respect to monotonicity of the parameters of these distributions.
Purpose
The purpose of this paper is to propose a novel lean management tool to provide a comprehensive and flexible evaluation model while converting customer voices into technical characteristics in lean implementations.
Design/methodology/approach
For this purpose, the proposed model was constructed by belief space-evaluations, quality function deployment (QFD) and analytic hierarchy process (AHP) in interval type-2 fuzzy (IT2F) environment. This model involves three phases: determining the linguistic weights and belief-based relations with their IT2F-sets, processing information about IT2F-based belief-evaluations and ranking the technical characteristics using the defuzzified belief-based relative importance values.
Findings
The proposed model was applied to automotive after-sales service in Turkey to demonstrate its use in lean service-decisions. This model was compared with its classical and type-1 fuzzy versions. The ranking-results of the proposed model differed from those of the other versions. The reason is that the IT2F-environment offers a sensitive and flexible evaluation of the model’s linguistic scales.
Research limitations/implications
Calculations in the proposed model may be quite involved for practitioners. An Excel-dashboard was created to simplify the computational complexity.
Practical implications
Researchers/practitioners can apply this model to any lean manufacturing/service implementation.
Social implications
Company managers/employees/customers can recognize their perception-mechanisms via belief space-evaluations and experience how uncertainty in the perception-mechanism affects their decisions.
Originality/value
The proposed model provides a new lean tool due to the Bayesian model combined with QFD-AHP in IT2F-environment. This model eliminates the ambiguity in conceptual change-based lean decisions.
Artan rekabet ortamında varlığını sürdürmek isteyen işletmeler için tedarikçi seçim ve değerlendirmeleri önemli bir yere sahiptir. İşletmeler uygun tedarikçi seçimi ile müşteri beklentilerini en iyi şekilde karşılamayı hedeflemektedir. Bu çalışmada, tedarikçi seçimi ve değerlendirmeleri için sezgisel bulanık kümelere dayalı bütünleşik bir yaklaşım önerilmektedir. Önerilen yaklaşım ile karar verici algı farklılıkları kaynaklı belirsizlikler ait olma ve ait olmama dereceleri ile detaylı şekilde incelenmektedir. Bu yaklaşım, inşaat sektöründe faaliyet gösteren bir işletmenin tedarikçi seçimi ve değerlendirmelerine uygulanmıştır. Uygulamada, ekonomik kriterlere dayalı karar verici öznel değerlendirmeleri ile işletme mevcut değerlendirme puanları birleştirilerek karma veritabanı oluşturulmuştur. Klasik ve bulanık öbekleme yaklaşımları ile tedarikçi firma sıralama ve sınıflandırmaları elde edilmiştir. Karma veritabanı için bulanık öbekleme yapısı %99,1; klasik öbekleme yapısı ise %94,4 doğruluk oranı ile oluşmuştur. Ayrıca, bulanık ve klasik öbekleme sonuçları içerisinde sadece tedarikçi değerlendirme puanlarına ait öbeklemenin, sırasıyla, %90,7 ve %74,1 doğruluk oranına sahip olduğu görülmüştür. Algı farklılıklarının tedarikçi seçimine yönelik karar almadaki etkileri önerilen bütünleşik yaklaşımla açıklanmıştır.
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