| 1. |
- Vanhatalo, Erik, et al.
(författare)
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Towards improved analysis methods for two-level factorial experiments with time series responses
- 2013
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Ingår i: Quality and Reliability Engineering International. - : Wiley. - 0748-8017 .- 1099-1638. ; 29:5, s. 725-741
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic processes exhibit a time delay between the disturbances and the resulting process response. Therefore, one has to acknowledge process dynamics, such as transition times, when planning and analyzing experiments in dynamic processes. In this article, we explore, discuss, and compare different methods to estimate location effects for two-level factorial experiments where the responses are represented by time series. Particularly, we outline the use of intervention-noise modeling to estimate the effects and to compare this method by using the averages of the response observations in each run as the single response. The comparisons are made by simulated experiments using a dynamic continuous process model. The results show that the effect estimates for the different analysis methods are similar. Using the average of the response in each run, but removing the transition time, is found to be a competitive, robust, and straightforward method, whereas intervention-noise models are found to be more comprehensive, render slightly fewer spurious effects, find more of the active effects for unreplicated experiments and provide the possibility to model effect dynamics. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.
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| 2. |
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| 3. |
- Vännman, Kerstin, et al.
(författare)
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Matematisk statistik
- 2020. - Tredje
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Bok (populärvet., debatt m.m.)abstract
- Denna bok är en omarbetning av Kerstin Vännmans tidigare bok Matematisk statistik från 2002. Boken syftar till att träna det statistiska tänkandet så att man kan förstå och använda några ofta förekommande statistiska metoder. Den är uppbyggd kring ett stort antal exempel och nya begrepp introduceras och motiveras med hjälp av inledande exempel.I boken behandlas bland annat enkla sannolikhetsresonemang, några vanligt förekommande fördelningar, till exempel binomial-, Poisson-, normal- och exponential-fördelningen, samt olika läges- och spridningsmått. Vidare behandlas punktskattningar, konfidensintervall (även jämförande situationer) och test. Den största förändringen jämfört med den tidigare boken är att regressionsanalys (både enkel och multipel) och flerdimensionella stokastiska variabler behandlas i denna bok. I regressionsanalysen ligger fokus på tillämpning med hjälp av statistisk programvara och tolkning av resultat.Boken vänder sig i första hand till studenter inom utbildningarna för civil- och högskoleingenjörer, men den är även lämplig för annan högskoleutbildning eller för självstudier. Till varje kapitel finns ett stort antal övningsuppgifter med svar. Dessutom finns ett separat kapitel med blandade övningar av varierande svårighetsgrad.
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| 4. |
- Albing, Malin, et al.
(författare)
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Elliptical safety region plots for Cpk
- 2011
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Ingår i: Journal of Applied Statistics. - : Informa UK Limited. - 0266-4763 .- 1360-0532. ; 38:6, s. 1169-1187
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Tidskriftsartikel (refereegranskat)abstract
- The process capability index C pk is widely used when measuring the capability of a manufacturing process. A process is defined to be capable if the capability index exceeds a stated threshold value, e.g. C pk >4/3. This inequality can be expressed graphically using a process capability plot, which is a plot in the plane defined by the process mean and the process standard deviation, showing the region for a capable process. In the process capability plot, a safety region can be plotted to obtain a simple graphical decision rule to assess process capability at a given significance level. We consider safety regions to be used for the index C pk . Under the assumption of normality, we derive elliptical safety regions so that, using a random sample, conclusions about the process capability can be drawn at a given significance level. This simple graphical tool is helpful when trying to understand whether it is the variability, the deviation from target, or both that need to be reduced to improve the capability. Furthermore, using safety regions, several characteristics with different specification limits and different sample sizes can be monitored in the same plot. The proposed graphical decision rule is also investigated with respect to power.
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| 5. |
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| 6. |
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| 7. |
- Albing, Malin, et al.
(författare)
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Skewed zero-bound distributions and process capability indices for upper specifications
- 2009
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Ingår i: Journal of Applied Statistics. - : Informa UK Limited. - 0266-4763 .- 1360-0532. ; 36:2, s. 205-221
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Tidskriftsartikel (refereegranskat)abstract
- A common practical situation in process capability analysis, which is not well developed theoretically, is when the quality characteristic of interest has a skewed distribution with a long tail towards relatively large values and an upper specification limit only exists. In such situations it is not uncommon that the smallest possible value of the characteristic is 0 and this also is the best value to obtain. Hence a target value 0 is assumed to exist. We investigate a new class of process capability indices for this situation. Two estimators of the proposed index are studied and the asymptotic distributions of these estimators are derived. Furthermore we suggest a decision procedure useful when drawing conclusions about the capability at a given significance level, based on the estimated indices and their asymptotic distributions. A simulation study is also performed, assuming that the quality characteristic is Weibull distributed, to investigate the true significance level when the sample size is finite.
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| 8. |
- Castagliola, Philippe, et al.
(författare)
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Average run length when monitoring capability indices using EWMA
- 2008
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Ingår i: Quality and Reliability Engineering International. - : Wiley. - 0748-8017 .- 1099-1638. ; 24:8, s. 941-955
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Tidskriftsartikel (refereegranskat)abstract
- In order to monitor unstable but capable processes Castagliola and Vännman have recently suggested a procedure based on an EWMA approach, called EWMA capability chart, for monitoring Vännman's Cp(u,v)-family of capability indices and showed how their proposed approach efficiently monitors capable processes by detecting a decrease or increase in the capability level. The goal of this paper is to investigate the efficiency of this capability chart in terms of ARL. The procedure used for computing this ARL is presented and simple guidelines for obtaining approximations to the optimal EWMA parameters are proposed.
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| 9. |
- Castagliola, Philippe, et al.
(författare)
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Monitoring capability indices using an EWMA approach
- 2007
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Ingår i: Quality and Reliability Engineering International. - : Wiley. - 0748-8017 .- 1099-1638. ; 23:7, s. 769-790
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Tidskriftsartikel (refereegranskat)abstract
- When performing a capability analysis it is recommended to first check that the process is stable, for example, by using control charts. However, there are occasions when a process cannot be stabilized, but it is nevertheless capable. Then the classical control charts fail to efficiently monitor the process position and variability. In this paper we propose a new strategy to solve this problem, where capability indices are monitored in place of the classical sample statistics such as the mean, median, standard deviation, or range. The proposed procedure uses the Cp(u,v) family of capability indices proposed by Vännman combined with a logarithmic transformation and an EWMA approach. One important property of the procedure presented here is that the control limits used for the monitoring of capability indices only depend on the capability level assumed for the process. The experimental results presented in this paper demonstrates how this new approach efficiently monitors capable processes by detecting changes in the capability level.
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| 10. |
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