Experimental Design and
Communicating Scientific Findings
Tyler Bassett and Tomomi Suwa
12.07.2011
Designing A Scientific Study
Thoughts on Experimental Design
Two types of studies
1) Observational
2) Experimental
Observational Study
-Observe subjects and measure variables of
interest without directly assigning treatments
to the subjects
-Less powerful – correlation does not imply
causation
Reasons for Observational Study:
- Experiment is logistically
impossible/impractical: rare species, stars,
river
- Experiment would violate ethical
standards: human disease
Manipulative Experiment
• Vary one factor explicitly and keep other
factors constant
• “Cleaner” than observational study, easier to
identify causative agent
When one thinks of “science,” this is
what they are thinking of!
Elements of Experimental Design
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•
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Independent vs. Dependent variable
Control
Replication
Randomization
Independent vs. Dependent variable
Independent Variable
– something that is intentionally changed or
manipulated by the scientist
Dependent Variable
– something that might be affected by the change
in the independent variable
– What is observed and measured
How do elevated soil nutrients affect plant growth ?
NO3-
PO3NH4+
What is an independent and dependent variable?
Effect of independent var. on dependent var.
Also referred to as predictor and response variables
Control
• The control and experimental groups must be
identical in every way except for the
introduction of a suspected causal agent into
the experimental group (s).
• Compare to an experimental group in a test of
a causal hypothesis – often to demonstrate
how much the causal agent changes the
dependent variable
How do elevated soil nutrients
affect plant growth ?
NO3-
PO3NH4+
What is the control here? What does it mean?
Control
Add N
Add P
Add N,P
Replication
• Repetition of an experiment to test the
validity of its conclusion
Control
Add N
Add P Add N,P
Randomization
- Assign treatment randomly to an
experimental group
- Roll dice, random numbers table, Excel:
“=rand()” function, www.random.org
- Eliminate researchers’ bias or judgment
Control
Add N
Add P Add N,P
Why randomization and replication
important?
• Reduce/eliminate self-deception and bias.
Control
Add N
Add P Add N,P
Why randomization and replication
important?
• Biased experimental design
Control
Add N
Add P Add N,P
Graphs
Dependent Var (unit)
Title: The Effect of the independent variable on the
dependent variable
Independent Var (unit)
Mean: shows differences
between treatment groups.
Error Bars: shows variability
of data around the mean.
Why control is
important in this case?
Plant Biomass (g)
Title: The Effect of Elevated Nutrients on the Plant growth
Control
Add
N
Add
P
Add
N, P
Soil Nutrients
Questions?
Communicating Scientific
Finding
How do scientists communicate Science?
Written Communication
• Research Article
• Book
• News paper
• Website/Blog
Oral Communication Visual Communication
• Presentation
•Poster
• Meeting
• Lecture ppt
• Lecture
• Interview (e.g. radio)
How do scientists communicate Science?
Written Communication
• Research Article
• Book
• News paper
• Website/Blog
Oral Communication Visual Communication
• Presentation
•Poster
• Meeting
• Lecture ppt
• Lecture
• Interview (e.g. radio)
In Research Article, Presentation & Poster
•Abstract
•Introduction
•Methods
•Results
•Conclusions
Let’s have a mini-symposium!
(20 min)
a) Focal Poster
-Presentation
-Content
b) Rest of the posters
Which poster is most catchy/attractive? Why?
Poster Evaluation
-Are research questions and hypotheses stated clearly?
-Does poster communicate the importance of the study?
-What are the dependent and independent variables?
-Are the tables and/or figures used to present the data effectively?
-Are the conclusions related back to the hypothesis, key scientific concepts,
and background research?
Which poster is most catchy/attractive?
Communicating Science:
Poster Presentation
*Borrowed some materials from: LiLynn Graves
Web and Graphic Designer, CCMR
Why poster?
• More interactive than writing a paper or
giving a talk
• More time to talk with people
• Can hang on the wall
• You can be creative!
Poster is basically a summary/outline
of a research paper
What to include?
•
•
•
•
•
•
•
•
Title, name
(Abstract)
Background/Intro
Methods
Results
Conclusion
Acknowledgement
(Citation)
What to include
• Title – 1-2 lines
• Name and affiliations
What to include (cont’d)
• Background
-Why important/interesting
-Hypotheses
*Get your audience interested in your work
• Methods
-Brief
-Include photos and illustrate experimental design, if
possible
What to include (cont’d)
• Results
-Include tables, figures, stats and brief description.
-Make sure your x and y axis are labeled clearly.
-Keep it simple!
Population size of Predator
and Prey through Time
Population Size
500
Prey
Predator
250
0
10
Days
20
What to include (cont’d)
• Conclusions
- Address your hypotheses
- Discuss why your results are
interesting/important
- “big picture”
- future direction
• (Literature cited)
• Acknowledgement
•
•
•
•
•
•
•
•
Title, name
(Abstract)
Background/Intro
Methods
Results
Conclusion
Acknowledgement
(Citation)
Organization
Organization
Colors
Be considerate for people with colour-vision deficiency
Poster in PowerPoint
• Determine the size of a poster
File -> page setup 46 x 38 inches
• Font size no smaller than size 40
After you make a poster draft…
• Print out a letter size draft and edit, edit, edit!
• Get feedback from your teacher/mentor and
peers
“Peer Edit”
Peer evaluation?
• Get feedback from different people
• Good practice to give/receive constructive
criticism
• Good motivation?
Questions, comments?