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Vita Ratnasari
Jurusan Statistika Institut Teknologi Sepuluh Nopember
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Modeling The Open Unemployment Rate Using A Ridge-Fourier Series Estimator In Nonparametric Regression Muthahharah, Sidratul; Budiantara, I; Ratnasari, Vita
KUBIK Vol 10 No 2 (2025): IN PRESS
Publisher : Department of Mathematics, Faculty of Science and Technology, UIN Sunan Gunung Djati Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15575/kubik.v10i2.55078

Abstract

Nonparametric regression is widely used to model relationships between variables when the functional form of the regression curve remains unspecified. The Fourier series estimator is effective for capturing periodic and complex nonlinear patterns. However, in multivariable settings, strong correlations among predictors may lead to multicollinearity, resulting in unstable parameter estimates due to the near-singularity of the design matrix. Although Fourier-based estimators have been extensively developed, their formulation has not explicitly addressed this issue. This study proposes a ridge-Fourier series estimator for nonparametric regression to obtain stable parameter estimation in the presence of multicollinearity. The estimator is derived within a penalized likelihood framework by incorporating a ridge penalty into the Fourier series representation and estimating the parameters. The oscillation and ridge penalty parameters are selected simultaneously using the Generalized Cross Validation (GCV) criterion. The proposed method is applied to the 2024 Open Unemployment Rate data covering districts and cities in West Java. The optimal model is obtained at the oscillation combination of [4, 4, 4, 2] with a ridge parameter of 0.0336, accompanied by a coefficient determination of 91.1%, indicating that the proposed ridge-Fourier estimator provides more stable estimation and improved predictive performance under multicollinearity conditions.
Poverty Modeling in East Nusa Tenggara Using Fourier Nonparametric Regression with Cosine–Sine Comparison and Hypothesis Testing Narita Yuri Adrianingsih; Andrea Tri Rian Dani; I Nyoman Budiantara; Vita Ratnasari; Yossy Candra; Bintang A. Banewang; Leti S. Gaimau
UNP Journal of Statistics and Data Science Vol. 4 No. 2 (2026): UNP Journal of Statistics and Data Science
Publisher : Departemen Statistika Universitas Negeri Padang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/ujsds/vol4-iss2/493

Abstract

Poverty is a complex multidimensional issue and remains a major development challenge in Indonesia, particularly in East Nusa Tenggara (NTT), which consistently records one of the highest poverty rates nationally. Conventional parametric approaches, such as linear regression, are often inadequate to capture the nonlinear and complex relationships between socioeconomic factors and poverty levels. Therefore, this study proposes a nonparametric regression approach based on Fourier series to model poverty in NTT. The novelty of this research lies in the systematic comparison between cosine-based and sine-based Fourier components within a nonparametric regression framework, combined with inferential statistical testing to identify significant determinants of poverty. The study uses cross-sectional data from 22 districts/cities in NTT for the year 2025. Model estimation is conducted using the Ordinary Least Squares (OLS) method, while the optimal oscillation parameter is determined using Generalized Cross-Validation (GCV). Model performance is evaluated using MSE, RMSE, MAPE, and coefficient of determination (R²). The results show that the cosine-based Fourier model with three oscillations outperforms the sine-based model, achieving MSE of 1.903, RMSE of 1.379, MAPE of 5.817%, and R² of 95.146%. Hypothesis testing indicates that all predictor variables significantly influence poverty levels both simultaneously and partially. These findings demonstrate that the Fourier nonparametric regression approach is highly effective in capturing complex and fluctuating poverty patterns, and it provides a more accurate and interpretable model for supporting targeted poverty alleviation policies.
Behavior of Trip Length Distribution Pattern due to the Variation of Trip Length Interval Determination Hitapriya Suprayitno; Nina Saraswati; Vita Ratnasari
IPTEK The Journal of Engineering Vol. 4 No. 1 (2018)
Publisher : Institut Teknologi Sepuluh Nopember

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/joe.v4i1.3561

Abstract

Transport Model is always needed and important for developing Transportation System Master Plan. Trip Distribution is one of the important parts of Transport Model, which is a result mathematical operation of trip generation and deterrence function. Trip Length Distribution Pattern is the foundation of Deterrence Function. The trip length distribution pattern can change due to the various trip length interval used. Analog to this, the Deterrence Function can also change. The research result indicate that the distribution pattern change significantly on trip length interval 1 to 3 km. For trip length interval of 4 to 8 km, the trip length distribution indicate the general characteristic of trip length distribution, i.e. the number of trips is high in short distance and getting down in the longer trip distance. The trip interval of 7 km gives the most accepted Tanner Deterrence Function.
Employee Engagement sebagai Strategi Peningkatan Kinerja Karyawan pada Pembangkit Listrik Joint Venture Indonesia–Tiongkok Nuraga Isma Affandi; Vita Ratnasari
Permana : Jurnal Perpajakan, Manajemen, dan Akuntansi Vol. 17 No. 3 (2025): Special Issue
Publisher : Faculty of Economics and Business, University of Pancasakti Tegal

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24905/permana.v17i3.1393

Abstract

Penelitian ini bertujuan untuk mengkaji peran employee engagement sebagai strategi peningkatan kinerja karyawan pada pembangkit listrik joint venture Indonesia–Tiongkok. Penelitian menggunakan pendekatan kuantitatif dengan metode survei terhadap karyawan operasional dan non-operasional. Analisis data dilakukan menggunakan Structural Equation Modeling–Partial Least Squares (SEM-PLS) untuk menguji hubungan antar variabel penelitian. Hasil penelitian menunjukkan bahwa employee engagement berpengaruh positif dan signifikan terhadap kinerja karyawan. Karyawan dengan tingkat keterikatan kerja yang tinggi mampu menunjukkan produktivitas, kualitas kerja, dan efektivitas pelaksanaan tugas yang lebih baik. Temuan ini menunjukkan bahwa peningkatan keterlibatan karyawan menjadi faktor penting dalam mendukung kinerja organisasi pada lingkungan kerja joint venture yang memiliki perbedaan budaya dan sistem manajemen. Penelitian ini memiliki keterbatasan pada penggunaan data cross-sectional dan lingkup penelitian yang terbatas pada satu pembangkit listrik. Meskipun demikian, hasil penelitian ini memberikan implikasi praktis bagi manajemen untuk memprioritaskan program peningkatan employee engagement sebagai strategi peningkatan kinerja karyawan. Penelitian ini memberikan nilai tambah dengan menyajikan bukti empiris mengenai peran employee engagement terhadap kinerja karyawan pada sektor ketenagalistrikan, khususnya pada pembangkit listrik joint venture Indonesia–Tiongkok.
Modeling The Open Unemployment Rate Using A Ridge-Fourier Series Estimator In Nonparametric Regression Sidratul Muthahharah; I Budiantara; Vita Ratnasari
KUBIK Vol 10 No 2 (2025): IN PRESS
Publisher : Department of Mathematics, Faculty of Science and Technology, UIN Sunan Gunung Djati Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15575/kubik.v10i2.55078

Abstract

Nonparametric regression is widely used to model relationships between variables when the functional form of the regression curve remains unspecified. The Fourier series estimator is effective for capturing periodic and complex nonlinear patterns. However, in multivariable settings, strong correlations among predictors may lead to multicollinearity, resulting in unstable parameter estimates due to the near-singularity of the design matrix. Although Fourier-based estimators have been extensively developed, their formulation has not explicitly addressed this issue. This study proposes a ridge-Fourier series estimator for nonparametric regression to obtain stable parameter estimation in the presence of multicollinearity. The estimator is derived within a penalized likelihood framework by incorporating a ridge penalty into the Fourier series representation and estimating the parameters. The oscillation and ridge penalty parameters are selected simultaneously using the Generalized Cross Validation (GCV) criterion. The proposed method is applied to the 2024 Open Unemployment Rate data covering districts and cities in West Java. The optimal model is obtained at the oscillation combination of [4, 4, 4, 2] with a ridge parameter of 0.0336, accompanied by a coefficient determination of 91.1%, indicating that the proposed ridge-Fourier estimator provides more stable estimation and improved predictive performance under multicollinearity conditions.
Implementation of the Fuzzy AHP, PROMETHEE II, and VIKOR Methods in Selecting Priority Projects in the Utilities Area of the PT ABC Refinery Dwiky Nugraha; Vita Ratnasari; Ridho Bayuaji; Ruri Agung Wahyuono
Journal Research of Social Science, Economics, and Management Vol. 5 No. 12 (2026): Journal Research of Social Science, Economics, and Management
Publisher : Publikasi Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.59141/jrssem.v5i12.1629

Abstract

The Utilities Plant at PT ABC’s LNG Plant has experienced declining reliability due to aging infrastructure. Data from the 2019–2024 period showed that 8 out of 13 Process Train operational failure cases were attributed to utility area failures, resulting in losses amounting to hundreds of billions of rupiahs. Capital investment evaluation (CAPEX) has traditionally focused primarily on financial indicators without incorporating non-financial parameters. This study applied a three-stage hybrid multicriteria decision-making (MCDM) model consisting of Fuzzy Analytical Hierarchy Process (FAHP) based on Buckley’s approach, PROMETHEE II, and VIKOR to optimize the selection of eight strategic project alternatives. The FAHP results identified Safety (35.06%) and Reliability (22.48%) as the highest-priority criteria. The PROMETHEE II method ranked HV Transformer Replacement (A3) as the first priority (net flow = +0.5308) and DCS Upgrade (A2) as the second priority (net flow = +0.5223). However, the Acceptable Advantage test in the VIKOR method indicated a very small difference in the compromise index (?Q = 0.0469 < 0.1429), suggesting that the ranking difference between the top alternatives was not sufficiently significant. Sensitivity analysis within the ±5% range resulted in shifts in the priority rankings, confirming the interdependence between power supply reliability and control automation systems. This study recommends HV Transformer Replacement (A3) and DCS Upgrade (A2) as co-priority project alternatives for implementation.
The Influence of Digitalization Readiness, Digital Mindset and Digital Culture on Digitalization Value in Multibusiness Companies Noer Aisyah Barlian; Vita Ratnasari
Jurnal Ekonomi Kreatif dan Manajemen Bisnis Digital Vol 4 No 2 (2025): NOVEMBER
Publisher : Transpublika Publisher

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.55047/jekombital.v4i2.1082

Abstract

In an era of increasingly massive technological disruption, companies are required to adapt and transform to remain relevant and competitive. Digital transformation has become a necessity, even for companies operating in regions with low technology adoption due to low human development indices. Therefore, multi-business companies undergoing digital transformation face various challenges, both internally and externally. This research aims to determine whether digitalization readiness, digital mindset, and digital culture influence digitalization value. The analysis method is quantitative, using a questionnaire that is subsequently analyzed with Structural Equation Modeling- Partial Least Square (SEM-PLS). The data used in this research is the result of a questionnaire survey aimed at employees in multi-business companies that use technology in their operational processes. The findings showed that Digitalization Readiness influences Digital Mindset and Digital Culture but does not have a direct effect on Digitalization Value. Digitalization Readiness has an effect on Digitalization Value through Digital Mindset, but not through Digital Culture. Ultimately, the key to maximizing the benefits of digitalization for multibusiness firms lies not only in being prepared and having a supportive culture, but also in cultivating a digital mindset. This mindset serves as the crucial path for creating value and should be the main focus for organizations aiming to fully embrace digital transformation.
Sales Performance Improvement Strategy Through the Technology Adoption of E -CRM Applications Dian Widiana Kuswara; Vita Ratnasari
Golden Ratio of Marketing and Applied Psychology of Business Vol. 6 No. 2 (2026): February - June
Publisher : Manunggal Halim Jaya

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.52970/grmapb.v6i2.2212

Abstract

This study aims to analyze the factors that influence the adoption of E-CRM applications in improving sales performance at PT PLN (Persero). This study uses an integrative approach between the Technology Acceptance Model (TAM) and the Unified Theory of Acceptance and Use of Technology (UTAUT) to identify factors that influence salespeople’s intention to use the system. The research method used is quantitative, and data analysis was carried out using the Partial Least Square Structural Equation Modeling (PLS-SEM) method. The results show that all proposed hypotheses are significantly accepted. Variables such as system adaptability, information quality, format quality, and ease of navigation influence the perception of ease and effectiveness of system use, which in turn influence perceived usefulness and behavioral intention. The main findings indicate that effort expectancy is the most dominant factor influencing intention to use, followed by performance expectancy, perceived enjoyment, and perceived usefulness. This study confirms that the success of E-CRM implementation depends not only on system quality but also on user perceptions of ease, usefulness, and user experience. The research results are expected to be the basis for developing strategies to increase E-CRM adoption to encourage more optimal sales performance in the PLN environment.
Co-Authors A. Tuti Rumiati Achmad Choiruddin Adatul Mukarohmah Agnes Tuti Rumiati Almira Qattrunnada Qurratu&#039;ain Ananda, Dwi Shinta Andrea Tri Rian Dani Anita Susanti Arif Khoirul Anam AVIANTHOLIB, IGAR CALVERIA Bachtiar, Raditya Fahmi Bastian, Endhy Bastian, Endhy Bintang A. Banewang Budiantara, I Cinde Pristi Kurnia Merdiko Citto Pacama Fajrinia Clara Dewanti Dani, Andrea Tri Rian Deby Lolita Permatasari Dedy Dwi Prastyo Dian Widiana Kuswara Dwi Maumere Putra Dwiky Nugraha Eko Wahyu Wibowo Elika Tantri Eling Anindita, Raden Erma Oktania Permatasari Fachrian Bimantoro Putra Farid Achmadi Farony, Rivan Faurizal Limansyah Fauziyah, Meirinda Febriliani Masitoh Feni Ira Puspita, Feni Ira Fithriasari, Kartika Fitriana, Dewi Fuad Achmadi Gita Prestalita Halistin, Halistin Haryono Haryono Hesikumalasari Hesikumalasari Hitapriya Suprayitno, Hitapriya Husna Miratin Nuroini I Budiantara I Nyoman Budiantara I Putu Artama Wiguna Ida Nur Indah Sari Insan Amalia Mutfi Ismaini Zain Karimah, Aprilia Fitri Khaerun Nisa&#039; Leti S. Gaimau Ludia Ni’matuzzahroh Made Ayu Dwi Octavanny Madu Ratna Marshiela, Jessie Reyna Maulidiah Nitivijaya Mokh. Suef Muhammad Aldani Zen Muthahharah, Sidratul NARITA YURI ADRIANINGSIH Ni'matuzzahroh, Ludia Nina Saraswati Nina Saraswati Nina Saraswati Nisa Andini Noer Aisyah Barlian Noer Aisyah Barlian, Noer Aisyah Novidianto, Raditya Nuraga Isma Affandi Nuroini, Husna Miratin Okka Kusumawati Asmoyo Pramaningrum, Dea Saraswati Purhadi Purhadi Putra, Fachrian Bimantoro Qonita Qurrota A&#039;yun R Sutjipto Reny Nadlifatin Retno Dewi Yulianti Rhifda Zukhrufi Ria Asih Aryani Soemitro Ridho Bayuaji Rifani Nur Sindy Setiawan Rizfanni Cahya Putri Rizky Amalia Yulianti Ruri Agung Wahyuono Santi Puteri Rahayu Setiawan Setiawan Shofi Andari Sidratul Muthahharah Sifriyani, Sifriyani Sitti Imaslihkah Suci Amalia Tandri Patih Taufiqotul Masrukha Tesha Nisva Tiza Ayu Virania Veniola Forestryani Vida Faiza Rochmah Wahyu Indri Astuti Wibawati Wibawati Winarni Kurniasari Yashintia Arien Epriliyanti Yollafie Asmara Yossy Candra Yovita Liana Salsabila Yuanita Damayanti Zen, Muhammad Aldani