Data Display

How to Effectively CommunicateYour Findings

Mary Purugganan, Ph.D.

maryp@rice.edu

http://www.owlnet.rice.edu/~cainproj/

Leadership & Professional Development Workshop

March 23, 2007

Deevey, E. S., Jr. Scientific American (1960) 194–204.

The population of the earth

0.0004% 0.05% 0.7%

Why improve your data presentation?

• To draw accurate conclusions

• To demonstrate professionalism

• To increase your credibility

• To better analyze, synthesize, and understand your data To see hidden relationships

To appreciate limitations, gaps

To formulate new questions

Today’s plan• Examine function and design

Tables

Scatter plots and line graphs

Bar charts, histograms, frequency polygons

Photographs, micrographs

Diagrams

Video clips

• Recognize differences in contexts Written documents

Visual presentations (posters, oral presentations)

• Discuss ethical issues in data display

• Revisit your own work

TablesFunction

Organize complicated data

Show specific results

Known (units) variable/unknown (units)

TablesDesign

Legend

• Place above table contents

• Must contain table number and title

• May contain a caption as well

Avoid rules (gridlines) in small tables

Use rules cautiously in large tables

• Choose narrow and/or gray lines

• Consider blocks of light color instead of rules

Example: Small table

Day, R.A. (1998) How to Write and Publish a Scientific Paper. Phoenix: Oryx Press

Decked heading

Example: Rules in large table

Rules should be narrow, faint, and unobtrusive

J. Donnell, Georgia Tech; http://www.me.vt.edu/writing/handbook

Example: Color bars in large table

Color bars aid readers who may have to, for example, look up and compare values often

J. Donnell, Georgia Tech; http://www.me.vt.edu/writing/handbook

Bivariate graphs

• X/Y axis: independent variable (what you control or choose to observe) vs. dependent variable

• Examples: Scatter plots/ line graphs

Bar graphs/ histograms

Scatterplots and line graphs• Function

Plot two variables; x and y represent actual, continuous space

Good for showing trends / relationships

• Design Avoid legends (keys) off to side in box

• Label lines (best for projected work), or

• Place key in caption or within graph (written documents)

Scatterplot with key in graph

Sanchez et al. (2004) Chem Eng J. 104:1-6

Line graph with key in legend

Day, R.A. (1998) How to Write and Publish a Scientific Paper. Phoenix: Oryx Press

Appropriate for written work, not projection

Revise: Distribution of Extensions based on Wi

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Fractional Extension

Frequency

0<Wi<5

10<Wi<15

Exercise: How would you revise?

Balanya et al. Science (2006) 313:1773.

Packed graphs: use with caution

Chmiola et al. Science (2006) 313:1760.

Ways to represent data sets

Valiela (2001) Doing Science: Design, Analysis, and Communication of Scientific Research. New York: Oxford University Press.

Ways to represent data sets

Valiela (2001) Doing Science: Design, Analysis, and Communication of Scientific Research. New York: Oxford University Press.

median

Upper/lower quartiles

Min

Max

Bar Graphs

Allow comparisons in values when the independent variable is a classification or category

Dependentvariable

Classification or category

Choose the right graph

If your variables are categorical (distinct, with no intermediates), you cannot plot with a line graph

Nonpoint Source News-Notes 43:5 (1995)

Histograms• Function

Plot frequency vs. intervals of values

Good for seeing shape of the distribution

Good for screening of outliers or checking normality

Not good for seeing exact values (data is grouped into categories)

• Design Bars should touch one another (unlike bar graphs)--

lower limit of one interval is also upper limit of previous interval

Use only with continuous data

Example: Histograms

Fig. 5. Frequency histograms of ΔP2/μ values using different step distances. At a step distance of 10 μ (a) the percent histogram is symmetric, i.e. positive and negative values have similar frequencies. At larger step distances the histograms become broader (50 μ) and then disintegrate (500 μ). Class size: 1 torr.

Baumgartl et al. (2002) Comparative Biochemistry and Physiology 132:75-85.

S. Hofferberth et al. Radiofrequency-dressed-state potentials for neutral atomsNature Physics 2, - pp710 - 716 (2006)

a, For the coherent splitting, a BEC is produced in the single well, which is then deformed to a double well. We observe a narrow phase distribution for many repetitions of an interference experiment between these two matter waves, showing that there is a deterministic phase evolution during the splitting. b, To produce two independent BECs, the double well is formed while the atomic sample is thermal. Condensation is then achieved by evaporative cooling in the dressed-state potential. The observed relative phase between the two BECs is completely random, as expected for two independent matter waves.

Exercise: how would you revise these histograms?

Schuck, P.J. et al. (2005) Chemical Physics. 318:7-11.

Fig. 2. (a) Histogram of total detected TPF photons from single-molecule time traces and an exponential fit to the distribution, yielding an e-1 value of 6024 ± 730 photons. A histogram of single-molecule TPF lifetimes of DCDHF-6 in PMMA is shown in (b). The lifetime distribution is fit to a Gaussian; fit parameters are given in the text.

Frequency Polygons• Function

Constructed from frequency tables

Visually appealing way of showing counts/ frequency

Better than histogram for two sets of data because the graph appears less cluttered

• Design Use a point (instead of

histogram bar) and connect the points with straight lines

May shade area underneath the line

http://www.olemiss.edu/courses/psy214/Lectures/Lecture2/lex_2.htm

Three-variable graphs

• Perspective graphs

• Contour plots

• See Doing Science: Design, Analysis, and Communication of Scientific Data (Valiela, 2001)

http://www.itl.nist.gov/div898/handbook/eda/section3/contour.htm

Kazhdan, D. et al. (1995) Physics of Fluids 7:2679-2685

No chartjunk!Graphical simplicity: keep “data-ink” to “non-data-ink” ratio high

Rate of seedling growth at three different temperatures

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Days of growth

Mean seedling height (mm)

20 C

25 C

30 C

Too much non-data ink

30oC

25oC

20oC

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Days of growth

Mean seedling height (mm)

Emphasis on data

No chartjunk!

• Gridlines

Rarely necessary

Better when thin, gray

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Series1

Series2

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• Fill patterns

Avoid moiré effects / vibrations

Gray shading is preferable to hatching

• Avoid 3-dimensional bars

Photographs• Function

Good for documenting physical observations

Usually qualitative but supported by quantitative data

• Design

Place title and caption below photograph(s)

Crop and arrange several photographs to facilitate understanding

Insert scale bars when necessary

Shahbazian et al., Neuron (2002)

C.R. Twidale (2004) Earth Sci Rev 67:159-218

Micrographs

Lambert et al. (2004) Virology 330:158-67

Fig. 2. GFP.S co-localizes with wild-type S at the ER. Shown is the intracellular distribution of GFP.S expressed either alone (squares a–c) or together with SHA (squares d–i) in COS-7 cells. Cells were fixed, permeabilized, and examined by fluorescence microscopy. (a, d, and g) GFP fluorescence (green); (b and e) immunostaining with a mouse antibody to PDI followed by AlexaFluor 494-conjugated goat anti-mouse IgG (red); (h) immunostaining with a mouse anti-HA antibody followed by AlexaFluor 494-conjugated goat anti-mouse IgG (red) to visualize SHA. Squares c, f, and i are the corresponding merged images so that overlapping red and green signals appear yellow. Ali et al. (1998) Thin Solid Films 323:105-109

Fig. 3. STM micrographs of Ag (100). (a) 0.1 Å~0.1 area. (b) Edge enhanced image of (a), (c) 500 ÅÅ~500 Å and (d)

100 ÅÅ~100 Å areas, respectively.

Diagrams & drawings

• Function

Show parts and relationships

Focus audience attention to what is essential

• Design

Use color to show relationships and draw eye

Avoid unintentional changes in proportion and scale

Leuptow, R.M. (June 2004) NASA Tech Briefs.

Video clips

• Function Show processes in real-time

Supplement online journal articles

May be qualitative but supported by quantitative data

• Design No conventions yet observed / published

Video clips

Shahbazian et al., (2002) Neuron 35:253-54.

Supplemental movie S2 online at:

http://www.neuron.org/cgi/content/full/35/2/243/DC1/

QuickTime™ and aH.263 decompressor

are needed to see this picture.

Design data display for your context

Written documents

Theses

Manuscripts

Reports

Visual presentations

Seminars/ oral presentation

Posters

Conventions for written documents

• Number and title (caption) each graphic Table 1. Xxxxxxx…

Figure 3. Xxxxxxx…

• Identify graphics correctly Tables are “tables”

Everything else (graph, illustration, photo, etc.) is a “figure”

Conventions for written documents

• Refer to graphics in the text “Table 5 shows…”

“… as shown in Figure 1.”

“… (Table 2).”

• Incorporate graphics correctly Place graphics close to text reference

Caption correctly• Above tables

• Below figures

Tips for written documents

• Design graphics for black-and-white printers and photocopies

• Figure and table captions can be long and informative (follow individual discipline and journal conventions)

• Remember audience when designing Journals: learn as much as possible about

audience to identify needs, areas of expertise

Thesis: design for “outside” committee member

Tips for visual presentations

Uniqueness of posters and oral presentations

• User is not a reader Is not able to assimilate great detail May not have time to process confusing data

• Oral communication accompanies what is printed / projected

• “Free” and “guaranteed” color Use color purposefully Avoid overuse of decorative color Avoid too much color (e.g., background fill) Avoid layering two colors of similar intensity (e.g., red on blue) Be sensitive to red/green color blindness

Replace titles and captions with message headings

Visual explanations

• Tag image with explanations

• Interpret (don’t just show) data (esp. on posters!)

Exercise: How would you revise for PPT?

Farchioni et al. Eur. Phys. J. C (2006) 47:461.

Ethics in data display

Putting data in the best light vs. trying to deceive through display

Data can be

• Distorted (perceived visual effect different from numerical representation)

• Misrepresented (particularly visual data)

• Cooked (selecting from among observations)

– Mendel?

• Trimmed (ignoring extreme values in a data set)

Distortion

Readers do not compare areas in circles correctly

(larger circle does not appear to have the increased area it actually does)

Number of people on Drug A

Number of people on Drug B

Distortion

3-dimensional graphs may fool the eye

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A B C

Series1

Cleveland’s experiments (1985)

Accuracy in perceiving graphical cues:

Position along axis

Length

Angle / slope

Area

Volume

Color / shade

most accurateperception

least accurateperception

How to avoid distortion

• Show enough data

• Be aware of potential sources of distortion Scale of graph (limits; log)

Placement of origin

Shape (length of axes)

Omission of data range in a continuum (implied continuum)

Linear and logarithmic scales

Schulze and Mealy (2001) American Scientist 89: 209.

Taking a log spreads out small values and compresses larger ones!

Ethics in display of visual data

Photographic data: Particularly vulnerable to trimming field of view selection

cropping

software (e.g., Photoshop) manipulation of contrast, brightness, etc.

• Editorial in Nature (Feb 23, 2006)

“In Nature’s view, beautification is a form of misrepresentation”

Concise guide to image handling in Guides for Authors (Nature family of journals)

http://www.nature.com/nature/authors/infosheets.html

Accessed 10/12/06

Summary

• Consider function when choosing visual

• Follow design conventions

• Adapt visual for context (written vs. visual)

• Design for audience

• Question your data selection and representation; avoid cooking, trimming, and distortion

Resources• Burnett, Rebecca (2001) Technical Communication. Fort Worth: Harcourt College

Publishers.

• Cleveland, W.S. (1985) The Elements of Graphing Data. Wadsworth.

• Technical Writing: Resources for Teaching (esp. Illustration section written by J. Donnell, Georgia Tech). Accessed 11/18/04. http://www.me.vt.edu/writing/handbook/

• Goodstein, David. Conduct and Misconduct in Science. Accessed 11/19/04. http://www.physics.ohio-state.edu/~wilkins/onepage/conduct.html/

• Klotz, Irving M. (1992) Cooking and trimming by scientific giants. FASEB J 6:2271-73.

• Not picture-perfect: Nature’s new guidelines for digital images encourage openness about the way data are manipulated. Editorial. (2006) Nature 439:891-92.

• Tufte, Edward R. (1983) The Visual Display of Quantitative Information. Cheshire, CT: Graphics Press.

• Valiela, Ivan (2001) Doing Science: Design, Analysis, and Communication of Scientific Research. New York: Oxford University Press.

SAMPLES

Fig.1: Loading plot for the first three PCs vs. the assay index

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fraction of LIVE cells

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% HEA/%AAm

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Cytocompatibility: Direct contact assay

Ave. Peak Force vs. Pulling Velocity for Various Spring Constants

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Pulling Velocity (nm/s)

Ave. Peak Force (pN)

Fernandez

k = 0.017 N/m

k = 0.068 N/m

k = 0.071 N/m

Log. (k = 0.017 N/m)

Log. (Fernandez)

Log. (k = 0.071 N/m)

Log. (k = 0.068 N/m)