• Journal of Korean Society of Industrial and Systems Engineering
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• v.23 no.59
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• pp.97-103
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• 2000

This study considers the design of life test sampling inspection plans by attributes for failure rate level qualification at selected confidence level. The lifetime distribution of products is assumed to be exponential. MIL-STD-690C and KS C 6032 standards provide this procedures. But these procedures have some questions to apply in the field. The cost of test and confidence level($1-{\beta}$ risk) are the problem between supplier and user. So, we suggest that the optimal life test sampling inspection plans using expected cost model considering product cost, capability, environmental test cost, etc.

• Communications for Statistical Applications and Methods
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• v.17 no.3
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• pp.319-326
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• 2010

In this paper, a new group sampling plan for the lot acceptance is proposed for the time truncated life test, which can be utilized when multi-item testers are implemented. The design parameters are found using the two-point approach such that the producer's and consumer's risks are satisfied simultaneously at the acceptable reliability level and the lot tolerance reliability level, respectively. The case of Weibull distribution is described to illustrate the procedure that can be used when the quality level is expressed by a multiple of the specified life. The advantage of the proposed plan is demonstrated by comparing with the existing plan in terms of the sample size required. The tables are constructed and some examples are given to illustrate the procedure developed here.

• Communications for Statistical Applications and Methods
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• v.18 no.4
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• pp.403-411
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• 2011

This paper deals with a group acceptance sampling plan for time truncated tests which are based on the total number of failures from the whole group assuming that the life time of an item follows the Dagum (inverse Burr) distribution. This study is developed when a multiple number of items as a group can be tested simultaneously in a tester. The minimum number of groups required for a given group size and acceptance number is determined such that the producer and consumer risks are satisfied simultaneously at the specified quality level, while the termination time and the number of testers are specified. Comparisons are made between the proposed plan and the existing plan on the basis of size of the groups. Two real examples are provided.

• International Journal of Reliability and Applications
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• v.17 no.1
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• pp.85-105
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• 2016

In this paper accelerated life testing is incorporated in quality control technique of acceptance sampling plan to induce early failures in high reliability products.Stress under accelerated condition can be applied in constant-stress, step-stress and progressive-stress or combination of such loadings. A ramp-stress results when stress is increased linearly (from zero) with time. In this paper optimum failure-censored ramp-stress accelerated life test sampling plan for log-logistic distribution has been formulated with cost considerations. The log-logistic distribution has been found appropriate for insulating materials. The optimal plans consist in finding optimum sample size, sample proportion allocated to each stress, and stress rate factor such that producer's and consumer's interests are safeguarded. Variance optimality criterion is used when expected cost per lot is not taken into consideration, and bilevel programming approach is used in cost optimization problems. The methods developed have been illustrated using some numerical examples, and sensitivity analyses carried out in the context of ramp-stress ALTSP based on variable SSP for proportion nonconforming.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.1
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• pp.76-85
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• 2007

A reliability acceptance sampling plan (RASP) consists of a set of life test procedures and rules for eitheraccepting or rejecting a collection of items based on the sampled lifetime data. Most of the existing RASPs areconcerned with the case where test items are available at the same time. However, as in the early stage ofproduct development, it may be difficult to secure test items at the same time. In such a case, it is inevitable toconduct a life test using sequentially supplied samples.In this paper, it is assumed that test items are sequentially supplied, the lifetimes of test items follow anexponential disthbution, failures are monitored continuously, arrival times of test items are known, and thenumber of test items at each arrival time is given. Under these assumptions, RASPs are developed by deter-mining the test completion time and the critical value for the maximum likelihood estimator of the mean lifetimesuch that the producer and consumer risks are satisfied. Then, the developed plans are compared to thetraditional Type-I censored RASPs in terms of the test completion time. Computational results indicate that thetest completion time of the developed RASP is shorter than that of the traditional Type-I censored plan in mostcases considered. It is also found that the superiority of the developed RASP becomes more prominent as theinter-arrival times of test items increase and/or the total number of test items gets larger.

• Communications for Statistical Applications and Methods
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• v.17 no.5
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• pp.725-731
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• 2010

Economic Reliability test plans(ERTP) are proposed considering that the life time of the submitted items follow the Pareto distribution of the second kind. For various specified acceptance number, sample size and producer's risk, a minimum test termination time is obtained. A comparison of proposed plan has been made with the existing plan developed by Aslam et al. (2010). The results are explained by tables and example.

• Journal of Korean Society for Quality Management
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• v.20 no.1
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• pp.22-32
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• 1992

This thesis compares life test acceptance sampling plans under lifetime has an exponential distribution. Various practical considerations may lead a user adopt a two-stage, or double sampling, test procedure. Hewett and Spurrier(1983) provided a survey of two-stage methods, as well as examples of experiments for which a two-stage procedure would be appropriate. The plans are compared in terms of the expected number of failures, and the expected time required to reach a dicision. Computational experiments are conducted and the results are tabulated to provide guidelines for selecting an appropriate plan for a given situation.

• Journal of Korean Institute of Industrial Engineers
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• v.20 no.1
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• pp.15-25
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• 1994

The Bayesian approach to reliability acceptance sampling has several advantages over the non-Bayesian approach. For instance, the former usually requires less amount of testing time and smaller sample sizes than the latter. In this article, a Bayesian acceptance sampling plan(ASP) based on a failure-free period life test is developed under the assumption of exponential lifetime distribution, and is compared with the corresponding Bayesian hybrid ASP in terms of the expected completion time. It is found that the proposed ASP tends to have a smaller expected completion time than the Bayesian hybrid ASP as the prior assessment of the reliability of a lot becomes optimistic, and vice versa. Tables of failure-free period Bayesian ASP's are also included.

• Journal of Families and Better Life
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• v.23 no.2 s.74
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• pp.149-157
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• 2005

The purpose of this study was to identify current housing status and housing awareness such as housing values, satisfaction, and preferences among households with one child. Data were obtained from a questionnaire completed by both husbands and wives living in metropolitan area and aged between 25 and 45. Selected variables were the age, education level, and employment status of housewives, ideal number of children, monthly income, plan to give birth, and so on. Using purposive sampling method, five hundred questionnaires were administered and 360 questionnaires were analyzed. In accordance with the questions related to housing values, housing satisfaction of respondents was examined. In order to compare the housing values, preferences, and satisfaction among diverse variables of respondents, mean, t-test, F test, Duncan's multiple range test, $x^2$ test, and factor analysis were used. The major findings of this study are as follows: First, there were significant differences in current housing type, tenure type, and floor area according to housewives' age, education level, monthly income, and plan to give birth. Interestingly, households not having a plan to give birth in the future were living in larger house than the households having a plan to give birth. Second, housing values of households with one child were divided into 4 factors-environmental comfort, economy and convenience, social status symbolism, and adequacy of space planning. Items related to privacy showed the biggest difference between housing values and housing satisfaction. Third, most of the respondents wanted larger house than current housing. However, the need for quality of housing including floor area and amenities was significantly higher among households not having a plan to give another birth than households having a plan to give birth in the future.

• Journal of the Korean Society of Clothing and Textiles
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• v.17 no.3
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• pp.359-366
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• 1993

The purpose of this study was to classify college women according to the general life style, to examine the differences in the characteristics of time consumption, and clothing purchasing behavior, and ultimately to verify the importance of the time variable in life style analysis. 449 subjects were gathered through convenience sampling method and, frequency, precentage, average, $x^2$-test, t-test, ANOVA, Duncan's multiple range test, Factor Analysis, Cluster Analysis were conducted for data analysis. Results of the study were as follows : 1. College women were classified into five subgroups by cluster analysis : fashion-pursuit group, home-intended group, outer-intended group, conservative-economy group, and passive-inactive group. 2. In case of time consumption patterns, significant differences were found according to the different groups in patronage of library and extra off-campus educational programs, participation in household duties, consumption patterns of leisure time and participation in clubs. 3. In case of clothing purchasing behavior, significant differences were found according to the different groups in clothing purchasing motives, information sources, purchasing plan, the number of visited stores, and the confirmation of labels.