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Unformatted text preview: Problem Set 2, Review • Lecture 12 Chapter 14: Process Control Charts Special Cause of Variation (Outlier): A measurement this far from the process mean is very unlikely if only expected variation is present Process Mean UCL LCL +3σ 3σ time Common Cause Variation: range of expected variability Special Cause of Variation (Outlier) Control chart shows if variation in data are due to: Common Cause Variation • Naturally occurring and expected fluctuations (normal variation in materials, tools, machines, operators, and the environment) • Reduced only by changing the process Special Cause Variation • Fluctuations or patterns not inherent to a process, often unusual events • Problems to be corrected or opportunities Data outside control limits or trends (Rules 1, 2, 3) Each dot corresponds to the sample statistic for a subgroup (one of the samples collected of the process output over time) Categorical variables (rooms ready or not) : sample proportion (rooms not ready) • PChart Numerical variables: range, mean (delivery times) • Range and Mean charts Process In Control • Process in control: points are randomly distributed around the center line and all points are within the control limits (only common cause variation) UCL LCL time Process Mean r This variation is normal for this process. • If variation is small enough for customer satisfaction, control chart is used to monitor the process • If the commoncause variation is too large, alter the process Process Out of Control: Rule 1 • One or more points outside control limits UCL LCL Process Mean Special Cause Variation: Outliers Special causes of variation must be identified • If detrimental to quality, remove • If increasing quality, incorporate into the process design Each dot corresponds to the sample statistic for a subgroup (one of the samples collected of the process output over time) Numerical variables: range, mean (delivery times) • Range and Mean charts r There was one sample of delivery times, whose mean was out of range Process Out of Control: Rule 2 § Eight or more points in a row on one side of the center line UCL LCL Process Mean Special Cause Variation: Pattern over Time Special causes of variation must be identified • If detrimental to quality, remove • If increasing quality, incorporate into the process design Each dot corresponds to the sample statistic for a subgroup (one of the samples collected of the process output over time) Numerical variables: range, mean (delivery times) • Range and Mean charts à 8 consecutive samples of delivery times are below the mean. à Why? (not a random variation in the process, potential opportunity) Process Out of Control: Rule 3 § Eight or more points moving in the same direction....
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This note was uploaded on 04/07/2011 for the course BUS 311 taught by Professor Reardon,j during the Spring '08 term at University of Hawaii, Manoa.
 Spring '08
 Reardon,J

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