Research Article
Penalized Likelihood Estimation for Current Status Data with Informative Censoring
Alhassan Faisal*,
Samuel Iddi,
Ezekiel Nii Noye Nortey,
Kwabena Doku-Amponsah
Issue:
Volume 9, Issue 3, September 2024
Pages:
39-57
Received:
23 March 2024
Accepted:
26 August 2024
Published:
29 October 2024
Abstract: Current status data occurs when failure time of subjects in a survival study is only known to be either less or greater than the censoring time. Thus, the failure time is either left – or right – censored. Analyzing data of this structure under the Cox Proportional Hazards model with dependent censoring assumption can be challenging. To address this, a Penalized Maximum Likelihood Estimation (PMLE) approach was proposed. The unknown baseline cumulative hazard functions for both the failure time and the censoring time were estimated using splines. The advantage of penalized approach over unpenalized method is that that the desired smoothness level of the functions are controlled by their respective penalty terms. The possible dependence between the failure and censoring times was accounted for using the gamma-frailty model. An easy to implement hybrid computational algorithm is proposed to estimate the PMLEs and the Bayesian technique was employed for the estimation of the variances of the parameters. Extensive simulation studies were conducted to assess the statistical properties of the PMLEs. It was observed that the realized estimators were not only consistent, asymptotically normal and efficient, but also, were robust to the number of knots chosen, the proportion of dependent censoring used and the frailty distribution employed. The proposed PMLE method was further applied to real data obtained from tumorigenicity experiment.
Abstract: Current status data occurs when failure time of subjects in a survival study is only known to be either less or greater than the censoring time. Thus, the failure time is either left – or right – censored. Analyzing data of this structure under the Cox Proportional Hazards model with dependent censoring assumption can be challenging. To address thi...
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Research Article
Identification of Resistance to Puccinia striiformisf. sp. tritici (Pst) in Some Commercial and Elite Bread Wheat Lines
Fikrte Yirga*
Issue:
Volume 9, Issue 3, September 2024
Pages:
58-66
Received:
18 September 2024
Accepted:
8 October 2024
Published:
29 October 2024
Abstract: Stripe rust is caused by Puccinia striiformisf. sp. tritici (Pst) threatening wheat production in Ethiopia. The emerged virulent stripe rust races at one point of the world spread to the rest of wheat-producing countries by the wind as well as human travels and damaged popular resistant wheat cultivars thereby posing food insecurity. However, wheat cultivars succumb to new Pst race (s) soon after their release from research centers. This study aimed to determine stripe rust resistance in some Ethiopian commercial and elite bread wheat lines. In 2017, a total of 37 commercial and elite bread wheat lines were exposed to stripe rust in under the disease hot spot areas (Kulumsa and Meraro) Arsi zone Oromia regional state. In the second year (2018), 22 promising lines consisting of 16 commercial bread wheat and 6 elite’s lines were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three Pst races. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR), and spike infection (SI) were considered. Of the 37 commercial and elite bread wheat lines, 19 (51.4%) exhibited lower or equal disease reaction compared to the resistant check (Enjoy) across locations and seasons. Eleven bread wheat lines showed both adult plant and seedling resistance. The 37 commercial wheat lines that showed field resistance was further exposed to three Pst races at the seedling stage and 11 exhibited seedling resistance to all races. This study has identified seedling and adult plant resistance in some commercial and elite bread wheat lines to the prevailing Pst races.
Abstract: Stripe rust is caused by Puccinia striiformisf. sp. tritici (Pst) threatening wheat production in Ethiopia. The emerged virulent stripe rust races at one point of the world spread to the rest of wheat-producing countries by the wind as well as human travels and damaged popular resistant wheat cultivars thereby posing food insecurity. However, wheat...
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