Experimental Design and Communicating Scientific Findings

Tyler Bassett and Tomomi Suwa12.07.2011

Designing A Scientific StudyThoughts 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

Reasons for Observational Study:

-Less powerful – correlation does not imply causation

- Experiment would violate ethical standards: human disease

- Experiment is logistically impossible/impractical: rare species, stars, river

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

• 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 ?

Effect of onindependent var. dependent var.

What is an independent and dependent variable?

NO3-

NH4+

PO3-

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 nutrientsaffect plant growth ?

What is the control here? What does it mean?

Add N Add P Add N,PControl

NO3-

NH4+

PO3-

Replication• Repetition of an experiment to test the

validity of its conclusion

Add N Add P Add N,PControl

Randomization

- Assign treatment randomly to an experimental group- Roll dice, random numbers table, Excel:

“=rand()” function, www.random.org

Add N Add P Add N,PControl

- Eliminate researchers’ bias or judgment

Why randomization and replication important?

• Reduce/eliminate self-deception and bias.

Add N Add P Add N,PControl

Why randomization and replication important?

• Biased experimental design

Add N Add P Add N,PControl

GraphsTitle: The Effect of the independent variable on the

dependent variable

Independent Var (unit)

Dep

ende

nt V

ar (u

nit)

Title: The Effect of Elevated Nutrients on the Plant growth

Soil Nutrients

Control Add N

Add P

Add N, P

Plan

t Bio

mas

s (g

)Mean: shows differences between treatment groups.Error Bars: shows variability of data around the mean.

Why control is important in this case?

Questions?

Communicating Scientific Finding

How do scientists communicate Science?

• Research Article • Book• News paper• Website/Blog

• Presentation• Meeting • Lecture• Interview (e.g. radio)

•Poster • Lecture ppt

Written Communication Oral Communication Visual Communication

How do scientists communicate Science?

• Research Article • Book• News paper • Website/Blog

• Presentation• Meeting • Lecture• Interview (e.g. radio)

•Poster • Lecture ppt

Written Communication Oral Communication Visual Communication

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 postersWhich 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 GravesWeb 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)

• Title – 1-2 lines• Name and affiliations

What to include

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!

Days

Popu

latio

n Si

ze

0 10 20

250

500

Population size of Predator and Prey through Time

Prey Predator

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 posterFile -> 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?