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How to Produce Statistical Graphics General Clinical Research Center August 15, 2005 Rachel Enriquez What are we going to talk about? Why should we care about statistical graphics? What is the theoretical framework for statistical graphics? When do we make statistical graphics?

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how to produce statistical graphics

How to Produce Statistical Graphics

General Clinical Research Center

August 15, 2005

Rachel Enriquez

what are we going to talk about
What are we going to talk about?
  • Why should we care about statistical graphics?
  • What is the theoretical framework for statistical graphics?
  • When do we make statistical graphics?
  • How can we produce good quality graphics?
communication of results is the last step in the scientific process
Communication of results is the last step in the scientific process
  • Many people can comprehend the results better by seeing them in a figure than they can by reading them in a table.
  • Do you have an opinion?
    • Graphics can help persuade.
    • Objectively correct graphics can call attention to the result you WANT the viewer to see.
get attention
Get Attention
  • Can you produce exceptional statistical graphics? (me neither)
  • Do you want people to know that you are committed to the scientific process?
  • If people understand your research, they’ll listen to you and do what you tell them to.
data visualization
Data Visualization
  • Visually encode the data.
  • Viewers decode the picture
    • Easy to figure out
    • Learn something new
    • See the right comparisons
hierarchy of visual perception
Hierarchy of Visual Perception

Position along common scale

Position along nonaligned scale

Length

Angle / Slope

Area

Volume

Color

aesthetics
Aesthetics
  • A personal matter
  • Unless you ask Tufte
  • Data / Ink ratio
  • Avoid 3-D
  • Fill patterns are bad
  • Obtain good resolution
  • Text can be small
    • (in print)
for publication in journals
For Publication in Journals
  • Data density is good.
  • Excellent resolution is required.
  • Color is difficult.
  • Column width is a consideration.
  • MS office is frequently not an option.
  • Too many tables!
a plot is better
A plot is better

Confounding variable

oral presentations
Oral Presentations
  • Data density should be moderate.
  • Color is available.
  • LABEL!
  • Hope you have interesting data
posters
Posters
  • Smaller audience
  • Experimentation is good.
  • Graphics will bring you customers!
how much time do you have
How much time do you have?
  • It is not easy.
  • There is no perfect, easy to use, cheap software that is going to solve your problems.
books are not very helpful
Books are not very helpful
  • Software changes quickly.
  • People use different software.
  • You want to do it NOW, not after reading for 5 hours.
  • Surfing the net is frequently useful.
vector graphics vs bitmaps
Vector Graphics vs Bitmaps
  • Vector graphics.
    • A set of instructions that tells the device how to display the document.
    • Adobe software is the most common way to edit vector graphics.
  • Bitmaps
    • Resolution depends on the size of the computer file.
    • Easy to open and publish on-line.
    • Generally not accepted for publication.
  • Vector graphics can be made into bitmaps.
  • Bitmaps cannot be made in vector graphics.
bitmaps compression and enlarging
Bitmaps, compression, and enlarging
  • Compression can be ‘lossy’
  • We are familiar with the grainy effect of enlargement.
software
Software
  • SPSS
    • Many chart options
    • Graphics can be edited
    • Can export vector graphics.
  • SAS
    • Known for poor graphics.
    • However, some people produce very good graphs with SAS.
    • Hope SAS improves and use something else for now?
slide35
Stata
    • Any comments?
  • R
    • It is free.
    • Produces good graphics that can be exported in various formats.
    • Infinitely customizable
    • Difficult for the novice statistician / programmer
    • R clinic
  • SyStat
  • EpiInfo
  • S+
  • Spotfire
  • Prism – also available in GCRC computer lab.
  • Others…..
sigma plot
Sigma Plot
  • Can be used with Excel and SPSS
  • Opens other data formats
  • Menu driven
  • Multiple graphics options
  • Easily produces compound graphics
  • Exports graphics in multiple formats.
ms office
MS Office
  • Windows Metafile is a vector graphic format.
  • Excel
    • More control over graphics
    • Limited selection of graph types
    • User typically provides the S.E.s and effect estimates.
  • PowerPoint
    • Surprisingly good at managing bitmaps.
    • If you already use it, then improve your graphics by applying aesthetic rules.
scanners
Scanners
  • Scanned figures are an option.
  • Good way to clean up figures from journals if you’re proficient in Photoshop
  • The bitmap resolution problem remains
  • Which file format and program will avoid lossy compression?
art software
Art Software
  • As a novice graphic preparator, I appreciate the ability to draw on graphs.
  • Can also ‘cover’ unwanted parts with white shapes.
  • Group the resulting collection of shapes and save as a picture.
slide41
Adobe Illustrator
  • Adobe Photoshop
    • These programs may seem counter-intuitive at first use.
  • Paint, MS office, etc.
    • Easy to use
    • Bitmap products.
call the experts
Call the experts
  • The Medical Illustrators at VUMC will improve your graphs.
    • $50/hr
    • Average graph is 20 minutes.
  • Grow your own group ‘expert’.