lecture 2-experimental design

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Experimental Design

Chapter 3

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Objectives

Define the scientific method Learn how to

design a scientific experiment calculate exposure times limit experimental error collect data analyze data present results write a technical report

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The Scientific Method

The process by which scientists, over time, attempt to build an accurate representation of the world.

Who we are and what we believe can influence our perceptions and our interpretations of the world around us.

As a result, scientists use standard procedures and criteria to minimize those influences (biases) when developing a theory.

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The Four Steps Observe and describe a phenomenon or

group of phenomena Formulate an hypothesis to explain the

phenomena Use the hypothesis to

Predict the existence of other phenomena, or

To predict quantitatively the results of new observations

Test the predictions by several independent experimenters and properly performed experiments

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Creating and Testing a Hypothesis Example: Radiation

What do you/we know about radiation exposure?

Create a hypothesis about radiation dose:

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Designing a Scientific Experiment How would you test your

hypothesis? What end result would you look

for? How might you bias your

experiment? How would you minimize it?

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Testing a Hypothesis

How would you know if you have proven or disproven your hypothesis?

How would you compare everyone’s results?

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Reporting Results

How would you report your results? Would you construct a table or a

graph? How would you label it/them?

How would you present your results?

Where do you go to find instructions?

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An Experiment: Radiation Effects on Pinto Beans

The experiment you are starting today will do four things: Demonstrate the use of one of our

irradiation facilities; Make you familiar with the unit of

absorbed dose (the gray or rad); Promote a class discussion on

experimental design; And, Allow you to see the effects of

radiation on plant growth.

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Irradiated Pinto Beans

Irradiated in the OSU Radiation Center 60Co gamma cell.

Each group of seeds was irradiated to different doses.

Neither the students nor the instructor knows the dose given to any of the groups.

The groups have been named: Marvin, Rhonda, Walter, Shiela, Betty, and Fred

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Radiation Doses

Absorbed Dose, rads

0 (control)

5,000

10,000

15,000

30,000

80,000

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GammaCell 220 60Co

A device for providing uniform radiation doses throughout a large volume

Approximately 8” h by 6” wide

Several small sources surround the irradiation chamber

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Exposure MapWithin the

Gammacell 220

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Planting Directions

Plant 5 beans (of the same dose group) in each Styrofoam cup

Label each cup with the name of the student group and the bean seed treatment (dose) group

Punch drainage hole(s) in each cup Fill cup approximately 3/4 full with dry

potting soil Using a pencil or stick, make holes in the

soil to a uniform depth (e.g., five bean seeds, five planting holes)

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Planting Directions, cont’d Lightly pat soil over beans Place styrofoam cups in the aluminum

baking pans.. Place baking pans on window sill Fill baking pans with water Periodically

water the plants in the same way. Do not let the soil dry out completely Do not over-water

observe the behavior and growth of the seeds.

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Science – It’s Great Stuff

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Summary

Design a scientific experiment Calculate exposure times Limit experimental error Collect data Analyze data Present results Write a technical report