Miin-Jye Wen

Single-Stage Multiple Comparison Procedures Under Heteroscedasticity

SYNOPTIC ABSTRACTGiven k (≥ 2) independent normal populations with unknown means and unknown (and possibly unequal) variances a single-stage sampling procedure for multiple comparisons with the largest normal mean and with a control, respectively, are proposed. The advantage of the single-stage procedure is to have design simplicity and to reach an exact solution. Simulation results indicate that the single-stage procedure appears to be a reasonable choice as compared to existing methods. Computer program and a numerical example are given.

Investigating the Relationships among E-Service Quality, Perceived Value, Satisfaction, and Behavioral Intentions in Taiwanese Online Shopping

As the online shopping market gradually grows in Taiwan, it is important to understand the diversity in various aspects of consumer behavior among Internet users. This paper examines the relationships among e-service quality, perceived value, satisfaction, and behavioral intentions for Taiwanese online shoppers. Based on a sample of 428 undergraduate students, a two-step structural equation modeling procedure is applied to perform an empirical test of the comprehensive model. The testing results show that, for the direct path, electronic service quality has a significant, positive influence on perceived value, satisfaction, and behavioral intentions. Also, perceived value directly influences customer satisfaction and behavioral intentions and satisfaction is an antecedent of behavioral intentions. For the indirect path, electronic service quality has a significant, positive influence on behavioral intentions through satisfaction and perceived value. Perceived value indirectly influences behavioral intentions via satisfaction. Managerial implications of these results are discussed.

Trends and determinants of informal and formal caregiving in the community for disabled elderly people in Taiwan

Although family caregiving for elderly people has been the backbone of long-term care in Taiwan, it is not clear whether informal help from family members has diminished in recent years due to changes in social structure and traditions. The objective of this study is to examine the trend and the factors influencing the use of informal and formal caregiving among disabled elders in the community of Taiwan. Data were drawn from three waves of the Taiwan Longitudinal Study on Aging (TLSA) (1999, 2003, and 2007) to examine the receipt of help with activities of daily living (ADLs) in a nationally representative sample of Taiwanese elderly people aged 65 and older. Results showed the trend in having at least 1 of 6 ADL limitations in the community increased mildly in the past decade but a significant rise in the use of paid help compared to informal help between 1999 and 2007. Factors associated with higher likelihood of paid help use included better socio-economic status and more ADLs. However, those living with spouse only were much less likely to use paid help than those living with adult children. Findings suggest that future long-term care (LTC) policy in Taiwan should focus more on providing elders who live alone or with spouse only additional caregiving resource. Given the rapid growth of foreign care workers as primary source of caregiving, the government needs further monitoring to promote care quality and also strategies to develop needs-led home and community based care.

Extension of three‐arm non‐inferiority studies to trials with multiple new treatments

Non-inferiority (NI) trials are becoming increasingly popular. The main purpose of NI trials is to assert the efficacy of a new treatment compared with an active control by demonstrating that the new treatment maintains a substantial fraction of the treatment effect of the control. Most of the statistical testing procedures in this area have been developed for three-arm NI trials in which a new treatment is compared with an active control in the presence of a placebo. However, NI trials frequently involve comparisons of several new treatments with a control, such as in studies involving different doses of a new drug or different combinations of several new drugs. In seeking an adequate testing procedure for such cases, we use a new approach that modifies existing testing procedures to cover circumstances in which several new treatments are present. We also give methods and algorithms to produce the optimal sample size configuration. In addition, we also discuss the advantages of using different margins for the assay sensitivity test between the active control and the placebo and the NI test between the new treatments and the active control. We illustrate the new approach by using data from a clinical trial.

Sample size determination in step‐up testing procedures for multiple comparisons with a control

Step-up procedures have been shown to be powerful testing methods in clinical trials for comparisons of several treatments with a control. In this paper, a determination of the optimal sample size for a step-up procedure that allows a pre-specified power level to be attained is discussed. Various definitions of power, such as all-pairs power, any-pair power, per-pair power and average power, in one- and two-sided tests are considered. An extensive numerical study confirms that square root allocation of sample size among treatments provides a better approximation of the optimal sample size relative to equal allocation. Based on square root allocation, tables are constructed, and users can conveniently obtain the approximate required sample size for the selected configurations of parameters and power. For clinical studies with difficulties in recruiting patients or when additional subjects lead to a significant increase in cost, a more precise computation of the required sample size is recommended. In such circumstances, our proposed procedure may be adopted to obtain the optimal sample size. It is also found that, contrary to conventional belief, the optimal allocation may considerably reduce the total sample size requirement in certain cases. The determination of the required sample sizes using both allocation rules are illustrated with two examples in clinical studies.

A studentized range test for the equivalency of normal means under heteroscedasticity

A studentized range test using a two-stage and a one-stage sampling procedures, respectively, is proposed for testing the null hypothesis that the average deviation of the normal means is falling into a practical indifference zone. Both the level and the power of the proposed test associated with the hypotheses are controllable and they are completely independent of the unknown variances. The two-stage procedure is a design-oriented procedure that satisfies certain probability requirements and simultaneously determines the required sample sizes for an experiment while the one-stage procedure is a data-analysis procedure after the data have been collected, which can supplement the two-stage procedure when the later has to end its experiment sooner than its required experimental process is completed. Tables needed for implementing these procedures are given.

On testing the bioequivalence of several treatments using the measure of distance

A studentized range test is proposed to test the hypothesis of bioequivalence of normal means in terms of a standardized distance among means. A least favourable configuration (LFC) of means to guarantee the maximum level at a null hypothesis and an LFC of means to guarantee the minimum power at an alternative hypothesis are obtained. This level and power of the test are fully independent of the unknown means and variances. For a given level, the critical value of the test under a null hypothesis can be determined. Furthermore, if the power under an alternative is also required at a given level, then both the critical value and the required sample size for an experiment can be simultaneously determined. In situations where the common population variance is unknown and the bioequivalence is the actual distance between means without standardization, a two-stage sampling procedure can be employed to find these solutions.

Optimal confidence interval for the largest mean of correlated normal populations and its application to stock fund evaluation

A single-sample sampling procedure for obtaining an optimal confidence interval for the largest or smallest mean of several correlated normal populations is proposed. It is assumed that the common variance is either known or unknown and the common correlation coefficient is a given non-negative value. The optimal confidence interval is obtained by maximizing the coverage probability with the expected confidence width being fixed at a least favorable configuration of means. Statistical tables of the critical values are calculated to implement the optimal confidence interval. Finally, this interval procedure is employed to estimate the mean return of the best stock fund among four diversified mutual funds in the United States from the years of 1977 to 2005. It has been found, with 95% confidence, that the best mutual fund has a mean return falling between nine and twenty-one percent, and the worst one has a mean return falling in a range from three and fifteen percent. Therefore, it can be concluded that stock fund investment in the U.S. stock market outperforms the long term inflation rate.

Noninferiority Studies with Multiple New Treatments and Heterogeneous Variances.

The objective of a noninferiority (NI) trial is to affirm the efficacy of a new treatment compared with an active control by verifying that the new treatment maintains a considerable portion of the treatment effect of the control. Compensation by benefits other than efficacy is usually the justification for using a new treatment, as long as the loss of efficacy is within an acceptable margin (NI margin) from the standard treatment. A popular approach is to express this margin in terms of the efficacy difference between the new treatment and the active control. Based on this approach and the realization that NI trials often comprise several new treatments, statistical procedures that simultaneously conduct NI tests of several new treatments have been developed. However, these procedures rely on the assumption that the variances of the treatments are homogeneous. In this article, we discuss the undesirable effect of using these procedures on the familywise Type I error rate when the treatment responses have heterogeneous variances. To alleviate this problem, we reveal potential procedures that are more appropriate. Further, a power study is conducted to compare the different procedures to provide guidance on the selection of adequate testing procedures in NI trials. Clinical examples are given for illustrative purposes.

The application of flow cytometry for evaluating biological aggressiveness of intracranial meningiomas

Meningiomas have classically been considered to include benign and atypical/anaplastic tumors. Despite the availability of clinical and pathologic parameters for prognostic prediction prognosis, the behavior of each meningioma may be difficult to predict. Here, we used DNA flow‐cytometric studies to predict biological tumor behaviors of intracranial meningiomas.