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level: Statistical process control (SPC)

Questions and Answers List

level questions: Statistical process control (SPC)

Question	Answer
- Control chats - Histograms - Pareto charts - Check sheets - Defect concentration diagrams - Scatter diagrams - Cause and effect diagrams	Seven tools of SPC
Measured values of a process characteristic is plotted over time to determine if the process remains in statistical control 1) Control charts for variables Measures a continuous quantity e.g. strength of material C-bar chart and r(ange) chart 2) Control chats for attributes Measures a discrete quantity e.g. dents on a fridge P(roportion) chat and c(ount) chart Less obvious signs - Trends or cyclical patterns in data - Sudden changes in average values - Points consistently near UCL or LCL - 8 consecutive points near UCL or LCL - 6 consecutive points where each is higher than the last	Control chats
Statistical graph with bars that represent different members of a populations with length indicating frequency or relative frequency Visually easy to detect - Shape of distribution - Any central tendencies - Approximations of mean and mode - Scatter in data	Histograms
- Special type of histogram where attributes are listed in order of frequency - Based on Pareto's Law "the vital few and the trivial many" - Aka the 80%-20% rule (80% of wealth is in 20% on pop) (80% of sales are made by 20% of customers)	Pareto charts
Data collection tool generally used in preliminary stages of studying quality problems e.g. defective item check sheet	Check sheets
- A drawing of the product in all relevant view, displaying the locations and frequencies of various types of defects - Useful for analysing causes of defects to identify the underlying causes	Defect concentration diagrams
- An x-y plot of data collected on two variables, where a correlation is suspected - The shape of the data often reveals a relationship	Scatter diagrams
- Fishbone diagram - A visual tool used to logically organize possible causes for a specific problem or effect by graphically displaying them in increasing detail, suggesting causal relationships among theories	Cause and effect diagrams
- Management commitment and leadership - Team approach to problem solving - SPC training for all employees - Emphasis on continuous improvement throughout organisation - A recognition and communication to recognise successful SPC efforts	Implementing SPC