ABSTRACT
The issue of various estimation techniques in constant partially accelerated life tests with complete data is the main subject of this research. The Chen distribution is regarded as an item's lifetime under use conditions. To estimate the distribution parameters and the acceleration factor, maximum likelihood estimation, least square estimation, weighted least square estimation, Cramér Von-Mises estimation, Anderson-Darling estimation, right-tail Anderson-Darling estimation, percentile estimation, and maximum product of spacing estimation are presented for classical estimation. For illustrative purposes, two real data sets are analyzed. The investigation of the two real data sets reveals that the suggested techniques are practical and can be used to solve some engineering-related issues. In order to compare the results of the several estimation techniques that have been offered based on mean square error and absolute average bias, a simulation study is presented at the end. When adopting the smallest values for mean square error and absolute average bias, this study demonstrates that maximum product of spacing estimation is the technique that is most effective among the alternatives in most cases.
ABSTRACT
In this work, we suggest a reduced distribution with two parameters of the modified Weibull distribution to avoid some estimation difficulties. The hazard rate function of the reduced distribution exhibits decreasing, increasing or bathtub shape. The suggested reduced distribution can be applied to many problems of modelling lifetime data. Some statistical properties of the proposed distribution have been discussed. The maximum likelihood is employed to estimate the model parameters. The Fisher information matrix is derived and then applied to construct confidence intervals for parameters. A simulation is conducted to illustrate the performance of maximum likelihood estimation. Four sets of real data are tested to prove the proposed distribution advantages. According to the statistical criteria, the proposed distribution fits the tested data better than some well-known two-and three-parameter distributions.
Subject(s)
Engineering , Likelihood Functions , Computer Simulation , Statistical DistributionsABSTRACT
A cluster of cases of severe influenzal disease was recognized in HIV-infected individuals during the 1997-1998 influenza season. Both primary influenza pneumonia and concomitant viral and bacterial pneumonia were found.
Subject(s)
HIV Infections/complications , Influenza A virus/isolation & purification , Influenza, Human/complications , Influenza, Human/epidemiology , Adult , Cluster Analysis , Female , Humans , Influenza, Human/diagnosis , Influenza, Human/virology , Male , Middle AgedABSTRACT
A cross-sectional study on 215 university female students aged 18-30 years was undertaken in 1993 to examine some factors associated with obesity among this group of females. Based on Body Mass Index (BMI), (wt/ht2), 19% of females were overweight and 9.8% were obese. The proportion of obesity was the highest in females aged 18 years (31%) compared to those aged 19 and 20 years and above (23.8% and 27.6%, respectively). Although there was no significant association between obesity and social factors studied, the prevalence of obesity was higher in non-national, those with educated mothers, having no housemaid, and having a family history of obesity. Skipping meals and snacks had no significant association with obesity, however, obesity was more prevalent among females who did not skip lunch. In contrast, females who ate afternoon snacks and supper were more likely to be obese than females who skipped these events. Median BMI for university females was higher than that reported in USA for the same age group, while median values for weight and mid-arm circumference for females studied were similar to that reported in their counterparts in Western countries.
