• Proceedings of the Korean Society for Quality Management Conference
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• 2006.11a
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• pp.211-216
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• 2006

Monitoring variability is a vital part of modem statistical process control. The conventional Shewhart Rand S charts address the setting where the in-control process readings have a constant variance. In some settings, however, it is the coefficient of variation, rather than the variance, that should be constant. This paper develops a chart, equivalent to the S chart, for monitoring the coefficient of variation using rational groups of observations.

• International conference on construction engineering and project management
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• 2020.12a
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• pp.257-264
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• 2020

Objective: To investigate test-retest reliability and responsiveness of Equivital Lifemonitor and photoplethysmography based wristwatch tools in assessing physiological parameters during a simulated fatigue task. Methods: Ten university students (Mean age, 30.6 ± 1.7 years) participated in this pilot study. Participants were asked to perform a 30-minute of a simulated fatigue task in an experimental setup in a lab. The physiological parameters (e.g., heart rate, heart rate variability, respiratory rate, electrodermal activity, and skin temperature) were measured at baseline and immediately after the fatigue task. An intraclass correlation coefficient (ICC2,1) was used to evaluate the test-retest reliability of each tool in assessing physiological measures. In addition, the responsiveness of each tool to measure changes from baseline to posttest was calculated using a standardized response mean. Results: The Equivital Lifemonitor has shown good to excellent test-retest reliability for the assessment of heart rate (ICC, 0.97), heart rate variability (ICC, 0.86), respiratory rate (ICC, 0.77), and local skin temperature (ICC, 0.76). However, photoplethysmography based wristwatch showed moderate to good test-retest reliability for the assessment of heart rate (ICC, 0.71), heart rate variability (ICC, 0.73), electrodermal activity (ICC, 0.80), and skin temperature (ICC, 0.72). A large standardized response mean (>0.8) indicates that both tools can capture the changes in heart rate, heart rate variability, respiratory rate, skin temperature, and electrodermal activity after a 30-minute of fatigue task. Conclusions: The Equivital Lifemonitor and photoplethysmography based wristwatch devices are reliable in measuring physiological parameters after the fatigue task. Additionally, both devices can capture the fatigue response after a simulated construction task. Future field studies with a larger sample should investigate the sensitivity and validity of these tools in measuring physiological parameters for fatigue assessment at construction sites.

• Journal of the Korea Society for Simulation
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• v.13 no.1
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• pp.41-50
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• 2004

The purpose of this paper is to analyse the manager's policy to maximize the profit in a multiple-server queueing facility with a limited queue capacity. We assume that the level of advertizing effects on the arrival rate of customers to the facility. The model without ‘word of mouth effect’ is assumed that the arrival rate is independent on the qualify of service level. We estimate the service quality by the balking rate of customers from system. We extend this to the model with ‘word of mouth effect’. To achieve the maximum profit, the most important factor is the considerably high utilization of facility for both models. Given service rate, we should maintain an effective arrival rate to some extent. To this end, among the available options, an increase of advertizing effort is more desirable than reducing the fee if the service value of customers remains unchanged. We also investigate whether the variability of service time has a significant impact on determining the optimal policy. The cost of service variability is not so expensive as that in a single server model due to the reduced variability of service times in a multiple-server model.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1987.10a
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• pp.20-20
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• 1987

• Proceedings of the Korean Society for Quality Management Conference
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• 1998.11a
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• pp.556-567
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• 1998

Robust design in industry is an approach to reducing performance variation of quality characteristic value in products and processes. Taguchi has used the signal-to-noise ratio(SN) to achieve the appropriate set of operating conditions where variability around target is low in the Taguchi parameter design. Taguchi has dealt with having constraints on both the mean and variability of a characteristic (the dual response problem) by combining information on both mean and variability into an SN. Many Statisticians criticize the Taguchi techniques of analysis, particularly those based on the SN. In this paper we propose a substantially simpler optimization procedure for robust design to solve the dual response problems without resorting to SN. Two examples illustrate this procedure. in the two different experimental design(product array, combined array) approaches.

• Proceedings of the Korean Society for Quality Management Conference
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• 2006.11a
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• pp.199-204
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• 2006

ANOVA is widely used for measurement system analysis. It assumes that the measurement error is normally distributed, which may not be seen in some industrial cases. In this study, the estimates of the measurement system variability and PTR (precision-to-tolerance ratio) are obtained by using weighted standard deviation for the case where the measurement error is non-normally distributed. The Standard Bootstrap method is used for estimating confidence intervals of measurement system variability and PTR. The point and confidence interval estimates for the cases with normally distributed measurement error are compared to those with non-normally distributed measurement errors through computer simulation.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1071-1078
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• 2006

Robust design of products or processes is a way to produce products or processes with less variability on condition that the product specification is met, so that the ratio of nonconforming products can be as minimized as possible. In such models as robust parameter design(RPD) originated by Taguchi and response surface methodology(RSM), the variances of noise variables are assumed to be measurable. However, there are circumstances in which the experimenters are unable to measure noise variables or perhaps are not aware of what the noise variables are. In this paper, it is demonstrated through an example that Taguchi's RPD approach can be conducted within the framework of the analysis of variability, with a view to a comparison of the two methods.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1999.06a
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• pp.53-80
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• 1999

Productivity and environmental conservation in nowadays trade-off and serious problem in agriculture. Precision farming is developing for solving the trade-off problem using systems approach and variable management. The systems approach is attributed to aiming at information-oriented agriculture, environmental-friendly sustainable agriculture, and complex system optimization . The variable management is composed of describing variability , variable-rate technology and decision support system. Three levels of technology development and three farming strategies are introduced for having a prospect. Describing the variability is the first step to promote it. Precision farming could be available for small scale farming as well as big scale farming. Paddy field precision farming will undergo in its distinctive way.

• Journal of Korean Society for Quality Management
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• v.35 no.1
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• pp.10-19
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• 2007

ANOVA is widely, used for measurement system analysis. It assumes that the measurement error is normally distributed, which nay not be seen in some industrial cases. In this study the estimates of the measurement system variability and PTR (precision-to-tolerance ratio) are obtained by using weighted standard deviation for the case where the measurement error is non-normally distributed. The Standard Bootstrap method is used foy estimating confidence intervals of measurement system variability and PTR. The point and confidence interval estimates for the cases with normally distributed measurement error are compared to those with non-normally distributed measurement errors through computer simulation.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.22 no.3
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• pp.225-232
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• 2019

Purpose: To evaluate intra- and inter-observer variability and guideline adherence amongst pediatricians in treating children aged between 4 and 18 years referred with recurrent abdominal pain (RAP) without red flags. Methods: The first part of the study is a retrospective single-center cohort study. The diagnostic work-ups of eight pediatricians were compared to the national guidelines. Intra- and inter-observer variability were examined by Cramer's V test. Intra-observer variability was defined as the amount of variation within a pediatrician and inter-observer variability as the amount of variation between pediatricians in the application of diagnostic work-up in children with RAP. Prospectively, the same pediatricians were requested to provide a report on their management strategy with a fictitious case to prove similarities in retrospective diagnostic work-up. Results: A total of 10 patients per pediatrician were analyzed. Retrospectively, a (very) weak association between pediatricians' diagnostic work-ups was found (0.22), which implies high inter-observer variability. The association between intra-observer diagnostic was moderate (range, 0.35-0.46). The Cramer's V of 0.60 in diagnostic work-up between pediatricians in the fictitious case implied the presence of a moderately strong association and lower inter-observer variability than in the retrospective study. Adherence to the guideline was 66.8%. Conclusion: We found a high intra- and inter-observer variability and moderate guideline adherence in daily clinical practice amongst pediatricians in treating children with RAP in a teaching hospital.