The Mechanics of Scientific Writing

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The Mechanics of Scientific Writing

W.S. Warner, Ph.D.

Day 1 Analysis and Structure Day 2 IMRAD and Argue

Day 3 Tables, Figures, Citation, Punctuation Day 4 Clarity and Cohesion

Day 5 Concision & Precision

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Program

Day 1

Analysis –critical thinking from note taking to brainstorming

Structure –outlining: analytical, comparison & contrast, argumentative Day 2

IMRAD – standard components of a publishable research manuscript Argue – how to argue and develop a thesis statement

Day 3

Tables and Figures – how to make your writing understood Citation –how to reference your sources.

Punctuation – how to make your writing accurate Day 4

Clarity – six principles of clear writing

Cohesion – how to make your writing fluid Day 5

Concision & Precision – how to make your writing tight and right Review

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Tables & Figures

to compare & contrast

1. When to use a table or figure

2. Components of tables and figures

3. Design tips

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Which format:

• Text

– Not all analyses or results warrant a Table or Figure – State simple results in text (data parenthetical)

In 2011, political prisoners in Libya increased significantly (125 p<0.001).

Seed germination was higher for plants in shallow-tilled soil (53 +/- 6

seeds) than for those in conventional plowed fields (14 +/- 3 seeds, t=11.2, p<0.001).

Text, Table or Figure?

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Table or Figure?

– Clearer and more concise than text – Supplement not duplicate text

– Time consuming to prepare

• Tables: compare numerical values and summarize data

– Number of subjects – Means

– Standard deviations

• Figures: show trends or patterns of relationship

– Graphs & diagrams – Photos & drawings – Schematics & maps

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How to refer to

Tables and Figures

• From the text

– All Tables and Figures must be referred to – Number sequentially (1, 2, 3, etc.)

– Focus on data point, relationship, trend – Refer parenthetically

In 2010, murder per capita was lowest in rural areas (Table 4), which supports Smith’s (2001 ) 15-year trend of rural crime (Fig. 7).

• Do not simply direct the reader

Table 1 shows the summary results for genetic variation of trout.

• Abbreviation

– "Figure" abbreviated "Fig.“

– "Table" not abbreviated – Both spelled out in titles

• Figure 1: Economic growth (1969-2010)…

• Table 1: Comparison of GPD…

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Placement of

Figures and Tables

• Consider your reader

– Readability is vital – Near first reference – Do not interrupt flow

• May be embedded in text, but

– Avoid breaking text into small blocks

– Better to have Fig. and Tables on their own pages

– End of Results or Discussion (for IMRAD), or appendix

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The Anatomy of a Table

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Table Structure

1. Title above the table

2. Units in column headings

3. Lines separate title, headings, data 4. Footnotes clarify

– statistical differences – data source (citation)

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Descriptive Titles

• Placement – think of the reader

• Lead the reader

• Read a table; read top down - above Tables

• Look at a figure; look up - beneath Figures

• Clear and complete

• results

• context: relationship displayed or treatment applied

• location (ONLY if a field experiment)

• explanation if needed to interpret results (e.g. footnotes)

• sample sizes and statistical tests as they apply.

Figure 1. Height frequency (%) of White Pines (Pinus strobus) in the UMB

Arboretum, Ås, Norway, before and after the 2010 ice storm. Before, n=137, after, n=133. Four trees fell during the storm and were excluded from post-storm survey.

• Do not restate the axis labels with "versus“

Figure 1: Poverty versus literacy.

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Title

Components

Data set changes mind set

1. Count

2. Comparison 3. Divisor

Murder Rates in EU Nations, 2010 (Homicides per 100,000 population) Murder Rates in EU Nations, 2010 (Homicides per 100,000 population)

US Public Health Care Expenditures, Per Capita: 1975-2004 (1999 dollars) US Public Health Care Expenditures, Per Capita: 1975-2004 (1999 dollars)

State Voter Turnout Rates, Presidential Elections: 1992-2008 (Votes cast/voting age population)

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Divisor

Rates, ratios, and per capita usually more meaningful than aggregate totals

Chicago 703 Detroit 43.0

New York 633 Chicago 25.6

Detroit 430 Philadelphia 23.3

Los Angeles 426 Dallas 23.1

Philadelphia 338 Phoenix 15.1

Houston 254 Houston 14.1

Dallas 252 Los Angeles 11.8

Phoenix 185 New York 8.6

San Antonio 89 San Antonio 8.1

San Diego 42 San Diego 3.5

source: Bureau of Justice Statistics: http://www.ojp.usdoj.gov/bjs/data/cities92.wk1

1a: Murders* in Ten Largest US Cities, 1998

1b: Murder Rates* in Ten Largest US Cities, 1998

*Murder and non-negligent

manslaughter per 100,000 population

*Murder and non-negligent manslaughter

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Sort data on the most

meaningful variable

Percent of 9-year-olds who watch more than 5 hours of

television per weekday

Percent of 9-year-olds who watch more than 5 hours of

televison per weekday

Canada 14.9 United States 21.5

Denmark 6.0 Spain 17.5

Finland 6.1 Canada 14.9

France 5.5 Netherlands 12.6

Germany 4.4 Ireland 11.8

Ireland 11.8 Italy 9.2

Italy 9.2 Finland 6.1

Netherlands 12.6 Denmark 6.0

Spain 17.5 France 5.5

Sweden 4.7 Sweden 4.7

United States 21.5 Germany 4.4

8a. Youth Television Watching

Source: Uri Bronfenburger, et. al. The State of Americans (New York: The Free Press, 1996); qtd. In

8b. Youth Television Watching

William Bennett, The Index of Leading Cultural Indicators (New York: Broadway Books, 1999), p. 230

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If you are reading this table

correctly, I’d be very surprised.

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Good examples of bad

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The Anatomy of a Line Graph

illustrate disparities, illuminate trends

particularly over time

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Anatomy of a Bar Graph

illustrates disparities, illuminates trends,

highlights comparisons

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Bar Graph

Compares single variable (Y) among groups (X )

• Title describes

– Variable measured (Y) – Treatment groups (X) – Sample size

– Statistical test

• treatment groups (pH) specified

• axis labels with units

• error bars with sample number

• statistical differences indicated by lines over bars

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Bar Graph

Columns touch if X-axis is continuous

• measured single variable on the Y axis

• groups (Habitat) on X axis

• second group variable (year) different bar

• key (within graph) defines bar fill

• error bars show +1 SD above the mean

• What’s wrong with the caption?

• A, B, C, AC are not explained.

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Frequency Histogram

Describes populations (size and age distributions) Columns touch for continuous X-axis

• Y axis indicates relative frequencies (%). Could be absolute frequency (number of stems)

• X variable (ht) divided into categories

• Sample size in the legend

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Compound Figures

• Same format, different data

A Harvested trees

B Non-harvested trees

• Title identifies data set (A, B)

• Text reads "...(Fig. 1b)"

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Which variable goes where?

• It depends

• dependent variable Y axis

• independent variable X axis

• tree height depends on age (age does not depend on height)

• Time is typically plotted as an independent variable.

• No independent variable?

• inter-dependence: no difference which variable is on which axis

• X,Y plot shows the relationship (rather than effect of one)

X

Y

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More figures

Photographs

• Source cited in title

• Sufficient resolution to photocopy

Charts

Figure 9. Aerial photo of the study site ca. 1949 and in 1998 (inset) showing the regeneration of the forest.

Photos courtesy of the USDA Field Office, Auburn, Maine.

• represent components of larger group (tribal hierarchy)

• steps in a process (flow-chart)

• schematics of an instrument

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Which to use?

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Pie Charts

indicate ratios, percentages

• Should rarely be used

• Difficult to discern size of pie slice relative to bar length

• 3-D pie charts add a

visual distortion

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Pie contests get messy

• Compare pies by adjusting the relative size

• Bad idea to use multiple pie charts to display more than one variable

• Made worse by "exploding" 3-D pies

• If pie charts show percentages, make sure they add up to 100

• Stay away from the fancy stuff

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Bars

• 3-D bar uses more ink, for what?

• 2-D uses data labels (492, 363, 381, 173) rather than a 3-D y-axis scale

– reduces 6 numbers to 4 – adds precision

• Strict application of ink-to-data:

present data as a table

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Principle 1: Clarity

What’s wrong with this table?

• Value units not clear.

• Share = % ?

•Title should be more descriptive.

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Good examples of bad

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From bad to worse

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Tips

• Less is more

– Simplify

– Half page/fig.

– Full page/compound fig.

• Highlight the important

• No pictures

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Figuratively speaking Science not Art

• Color

– Can distinguish data sets

– Photocopy will lose information

– Never use color simply because it is pretty

• Bars twice as wide as gaps

• Include

– Error bars (SD or SEM) when plotting means – Tick marks

• Major divide range of values

• Minor subdivide in logical units

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Figures don’t lie…

UNICEF

• Purports gap between rich and poor countries is increasing

• Per capita GNP of wealthiest countries almost doubled ($12,000 to $26,000)

• Has middle or low income countries GNP doubled?

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…but liars do figure.

ODA (Official Development Assistance)

• Arrows show declining donation, growing wealth

• $18 drop not big gray arrow, but little line

• Relative to GNP, ODA has not changed.

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Summary – check list

 Refer to the point you want to make

 Do not repeat information

 Number sequentially (in chapters: Fig. 2.1, 2.2, 2.3)

 Cite sources

Fig. 1 is taken from Smith (2004)

Table footnote: Data adapted from Smith et al. (2009)

 Legend tells readers what they are looking at

 Acid test

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"Acid Test" for

Tables and Figures

• Readability is critical – strive for simplicity

• Ask a colleague: Does it make sense?

• Must stand alone and be interpretable

• Must be understood by its title

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Interactive figures

http://www.ted.com/talks/lang/eng/hans_rosling_reveals_new_insights_on_poverty.html http://www.ted.com/talks/hans_rosling_shows_the_best_stats_you_ve_ever_seen.html