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1. |
Editorial: 25 years of applied statistics |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 3-22
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ISSN:0266-4763
DOI:10.1080/02664769823278
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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2. |
A statistical signalling model for use in surveillance of adverse drug reaction data |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 23-40
EricM. Hillson,
JaxkH. Reeves,
CharlotteA. Mcmillan,
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摘要:
This paper presents a statistically superior lag-adjusted model for detecting increased frequency of reports of adverse drug event (ADE) rates. The effect of a significant lag time between ADE occurrence and report dates is studied. The approach in this paper to analyzing ADE data of this nature involves proposing a statistical model that utilizes a lag density function. The statistical method proposed was the development of an 'exact' procedure to monitor drugs that have a low incidence of ADEs. The approach determines statistically whether a change in the frequency of a specific ADE exists between two predetermined time intervals. There exist immense public health implications associated with the early detection of serious ADEs. The reduced risk of unfavorable outcomes associated with medication therapy is the goal of all involved. Simulated illustrations and discussion are provided, along with a detailed FORTRAN program used to implement the newly suggested lag-adjusted procedure.
ISSN:0266-4763
DOI:10.1080/02664769823287
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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3. |
Optimal design of accelerated life tests under modified stress loading methods |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 41-62
Sang-Jun Park,
Bong-Jin Yum,
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摘要:
Most of the previous work on optimal design of accelerated life test (ALT) plans has assumed instantaneous changes in stress levels, which may not be possible or desirable in practice, because of the limited capability of test equipment, possible stress shocks or the presence of undesirable failure modes. We consider the case in which stress levels are changed at a finite rate, and develop two types of ALT plan under the assumptions of exponential lifetimes of test units and type I censoring. One type of plan is the modified step-stress ALT plan, and the other type is the modified constant-stress ALT plan. These two plans are compared in terms of the asymptotic variance of the maximum likelihood estimator of the log mean lifetime for the use condition (i.e. avar\[ln (0)]). Computational results indicate that, for both types of plan, avar\[ln (0)] is not sensitive to the stress-increasing rate R, if R is greater than or equal to 10, say, in the standardized scale. This implies that the proposed stress loading method can be used effectively with little loss in statistical efficiency. In terms of avar\[ln (0)], the modified step-stress ALT generally performs better than the modified constant-stress ALT, unless R or the probability of failure until the censoring time under a certain stress-increasing rate is small. We also compare the progressive-stress ALT plan with the above two modified ALT plans in terms of avar\[ln (0)], using the optimal stress-increasing rate R* determined for the progressivestress ALT plan. We find that the proposed ALTs perform better than the progressivestress ALT for the parameter values considered.
ISSN:0266-4763
DOI:10.1080/02664769823296
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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4. |
Robustness of the t and U tests under combined assumption violations |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 63-74
JohnM. Stonehouse,
GuyJ. Forrester,
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摘要:
When the assumptions of parametric statistical tests for the difference between two means are violated, it is commonly advised that non-parametric tests are a more robust substitute. The history of the investigation of this issue is summarized. The robustness of the t -test was evaluated, by repeated computer testing for differences between samples from two populations of equal means but non-normal distributions and with different variances and sample sizes. Two common alternatives to t -Welch's approximate t and the Mann-Whitney U -test-were evaluated in the same way. The t -test is sufficiently robust for use in all likely cases, except when skew is severe or when population variances and sample sizes both differ. The Welch test satisfactorily addressed the latter problem, but was itself sensitive to departures from normality. Contrary to its popular reputation, the U -test showed a dramatic 'lack of robustness' in many cases-largely because it is sensitive to population differences other than between means, so it is not properly a 'non-parametric analogue' of the t -test, as it is too often described.
ISSN:0266-4763
DOI:10.1080/02664769823304
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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5. |
Expected experiment times for the Weibull distribution under progressive censoring with random removals |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 75-83
Siu-Keung Tse,
Hak-Keung Yuen,
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摘要:
This paper considers the expected experiment times for Weibull-distributed lifetimes under type II progressive censoring, with the numbers of removals being random. The formula to compute the expected experiment times is given. A detailed numerical study of this expected time is carried out for different combinations of model parameters. Furthermore, the ratio of the expected experiment time under this type of progressive censoring to the expected experiment time under complete sampling is studied.
ISSN:0266-4763
DOI:10.1080/02664769823313
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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6. |
Estimation of HIV seroconversion and effects of age in the San Francisco homosexual population |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 85-102
Wai-Yuan Tan,
Si Chin Tang,
Sho Rong Lee,
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摘要:
Using San Francisco city clinic cohort data, we estimate the HIV seroconversion distribution by both non-parametric and parametric methods, and illustrate the effects of age on this distribution. The non-parametric methods include the Turnbull method, the Bacchetti method, the expectation, maximization and smoothing (EMS) method and the penalized spline method. The seroconversion density curves estimated by these nonparametric methods are of bimodal nature with obvious effects of age. As a result of the bimodal nature of the seroconversion curves, the parametric models considered are mixtures of two distributions taken from the generalized log-logistic distribution with three parameters, the Weibull distribution and the log-normal distribution. In terms of the logarithm of the likelihood values, it appears that the non-parametric methods with smoothing as well as without smoothing (i.e. the Turnbull method) provided much better fits than did the parametric models. Among the non-parametric methods, the EMS and the spline estimates are more appealing, because the unsmoothed Turnbull estimates are very unstable and because the Bacchetti estimates have a longer tail. Among the parametric models, the mixture of a generalized log-logistic distribution with three parameters and a Weibull distribution or a log-normal distribution provided better fits than did other mixtures of parametric models.
ISSN:0266-4763
DOI:10.1080/02664769823322
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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7. |
Chain sampling plan for variables inspection |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 103-109
K. Govindaraju,
S. Balamurali,
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摘要:
This paper extends the concept of chain sampling to variables inspection when the standard deviation of the normally distributed characteristic is known. A discussion of the shape of the known sigma single-sampling variables plan is given. The chain sampling plan for variables inspection will be useful when testing is costly or destructive.
ISSN:0266-4763
DOI:10.1080/02664769823331
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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8. |
Best efficient estimates of the intensity function of the power law process |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 111-120
Hongzhu Qiao,
ChrisP. Tsokos,
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摘要:
We develop a general statistical procedure to obtain linearly the best efficient estimate of existing estimations of the parameter of a probability process. This procedure is used to obtain the best efficient estimates of the shape parameter, the intensity failure function and its reciprocal of the power law process. These estimates are important in the study of reliability growth modelling. The effectiveness of our findings is illustrated analytically and numerically, using real data and numerical simulations.
ISSN:0266-4763
DOI:10.1080/02664769823340
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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9. |
Graphical approach to model adequacy based on exact and near replicates |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 121-129
M. Yahyah,
A. Baines,
D. N. Joanes,
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摘要:
In this paper, we present an intuitive graphical approach to model validity, which, although to some extent subjective, can be extremely valuable for both presentation and interpretation purposes. In particular, the idea behind such a procedure arises naturally through the generation of a sequence of elements derived from the residuals about a fitted graduating function, based on datum points that are identical or that are relatively close together in a multi-dimensional factor space.
ISSN:0266-4763
DOI:10.1080/02664769823359
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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10. |
Genotypic performance over environmental arrays: A non-linear grouping protocol |
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Journal of Applied Statistics,
Volume 25,
Issue 1,
1998,
Page 131-143
J. E. Toler,
P. M. Burrows,
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摘要:
A non-linear model for examining genotypic responses across an array of environments is contrasted with the 'joint regression' formulation, and a rigorous approach to hypothesis testing using the conditional error principle is demonstrated. The model is extended to cater for situations where single straight-line response patterns fail to characterize genotypic behaviors over an environmental array: a combination of two straight lines, with slope in below-average and in above-average environments, is offered as the 1 2 simplest representation of convex and concave patterns. A protocol for classifying genotypes according to the results of hypothesis tests, i.e. H( = ) and H( = = = 1), is 1 2 1 2 presented . A doubly desirable response pattern is convex ( < 1< ), while a doubly 1 2 undesirable pattern is concave ( > 1> ). 1 2
ISSN:0266-4763
DOI:10.1080/02664769823368
出版商:Taylor & Francis Group
年代:1998
数据来源: Taylor
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