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Data=Facts Which Convey Information
(for example, the PREZHITE data set)
Statistics: The Science of Data
Displaying Data
o
Frequency Histogram
: shows
Data Distribution
: static pattern of variation.
o
Time Series Plot (or Line Plot)
: shows pattern of variation evolving over time.
Stationary Processes
o Pattern of variation does not change as more data are taken.
o
To assess stationarity
data must be plotted versus time.
o
A Moving Average
Removes extraneous variation.
Helps show changes in average value over time.
Causes of Variation
o
Common Causes
: Systemic
o
Special Causes
: Periodic and unpredictable
See line plot of data set PRIMER.
Graphical Tools for Identifying Causes of Variation
o
Line or Time Series Plots
o
Stratified Plots
o
Process Flow Diagrams
o
Ishikawa Diagrams
Application: Gage R&R
o
Repeatability
: consistency of gage in repeated measurements by same operator on same part.
o
Reproducibility
: variation between different operators.
See data sets BOLTS, BOLTS1.
About this document ...
Joseph D Petruccelli
5/27/1998