II. Graphical Displays of Data Like many other things, statistical analysis can suffer from garbage in, garbage out This often happens because no one bothered to look at the data. Simple data displays can convey a lot of information. A. Stem-and-Leaf Displays Purpose: To provide a basis for evaluating the “shape” of the data without the loss of any information.
II. Graphical Displays of Data Like many other things, statistical analysis can suffer from garbage in, garbage out This often happens because no one bothered to look at the data . Simple data displays can convey a lot of information. A. Stem-and-Leaf Displays - PowerPoint PPT Presentation
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II. Graphical Displays of Data
Like many other things, statistical analysis can suffer from garbage in, garbage out
This often happens because no one bothered to look at the data.
Simple data displays can convey a lot of information.
A. Stem-and-Leaf Displays
Purpose: To provide a basis for evaluating the “shape” of the datawithout the loss of any information.
1. Basic Stem and Leaf Display
This technique is best illustrated by an example.
Pencil lead is actually a ceramic matrix filled with graphite.
A measure of the quality of many ceramic bodies is the porosity.
Porosity is a measure of the void space in the body.
The following data set represents the result of a porosity test on“good” pencil lead
Box Plots can also be used to analyze designed experiments. When there are categorical factors, the design can be “unstripped” and analyzed using parallel box plots.
Example: Consider an experiment to study the influence of operating temperature and glass type on light output.
Temp. Glass Type Low High 550 1380 565 1365 A 540 1384 575 1374 584 1379 545 880 582 891 B 576 864 553 875 574 883
The resulting box plot is given below.
The box plots show that a higher temperature yields higher light output. Also at the low temperature, glass type does not affect light output, but at the high temperature, glass type A produces higher light output.
Light
Outp
ut
Temp.Glass
HighLowBABA
1050
1000
950
900
850
800
750
700
Importance of Box Plots:
Boxplots allow us to tell at a glance:
1. center
2. spread
3. outliers
Other important data displays:
• histograms
• time plots
We generally use software to generate all data displays.
The instructor should do an class demonstration using the software selected by the instructor.