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Scientific Method

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Posing and Testing Methods

• Observation

• Question

• Hypothesis

• Prediction

• Experiment

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Posing and Testing Methods

• Observation: The flashlight doesn’t work

• Question: What’s wrong with the flashlight

• Hypothesis: The batteries are dead

• Prediction: If the batteries are dead and you replace them with new ones, then the flashlight will work.

• Experiment: Replace the batteries.

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Now you try:

• Observation :

• Question :

• Hypothesis :

• Prediction :

• Experiment :

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What Makes A

Good Biology Experi-ment?

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1. Ask a testable Question.

Example:

Does watching T.V. make you fail Biology class?

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2. Form a Hypothesis.

• Educated guess.

•Never in a question form.

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3. Design a Controlled Experiment:

A test where only one variable is being changed at

one time.

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What is involved in designing a good experiment?

• Set up a Control Group• Set up a Experimental Group• Determine which is the Independent Variable• Determine which is the Dependent Variable• Repeat the experiment to verify results• Use a lot of sample groups in order to get the best

indication of results• Consider all Safety Issues• Eliminate Experimental Error• Prevent Bias• AND REPEAT

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3a. Control Group

The group that does not receive the “treatment”

(business as usual)

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3b. Experimental Group

The group that receives the “treatment”

Only one variable is changed at a time.

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3c. Independent Variable (manipulated variable)

The variable that is deliberately changed in an

experiment.

(it is what I (the scientist) changes from one group to the other)

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3d. Dependent Variable (or responding variable)

The variable that changes because the independent

variable changed.

Depends on the Independent Variable

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3e. Replication: How many times an experiment is done.

3f. Sample Size:

The number of control & experimental groups.

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3g. SAFETY!!!•For the researcher

• For the Environment (Inside or outside labs)

• For the test subjects

•(like animals)

Two types of Error

• Operator Error– What the scientist did wrong

• Bias• Falling Asleep during data collection• Inaccurate measurements

• Equipment Error– What went wrong with equipment

• Dirty Glassware• Equipment with incorrect increments for measurement

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SET UP AN EXPERIMENT

• Shoe Brand’s Effect on Speed

• ** Add: “Dependent Variable: _____________”

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Early Experiments

in Transportation

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Farside Cartoon: G. Larson “Notice all the

computations, theoretical scribblings,

and lab equipment,

Norm…Yes, curiosity

killed these cats.”

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3h. Identify sources experimental error.

•Bias: Preconceived ideas that influence experimenter.

•Operator or Equipment failure.

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3i. How can you prevent bias??

•Placebos- ½ test subjects given control or fake variable

•Blind-Study- test subjects don’t know if they have placebo or real

•Double-Blind- test subjects and scientists don’t know who has placebo or real

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4. Collect Data.

Think about how best to set up a data sheet.

Will your data be qualitative or quantitative?

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5. Analyze data.

Create a graph, chart, or map to organize collected

data.

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6. Form conclusions.

What patterns do you see?

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7. Repeat Experiment.

Do not change any variables!

VALIDITY

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What is involved in designing a good experiment?

• Set up a Control Group• Set up a Experimental Group• Determine which is the Independent Variable• Determine which is the Dependent Variable• Repeat the experiment to verify results• Use a lot of sample groups in order to get the best

indication of results• Consider all Safety Issues• Eliminate Experimental Error• Prevent Bias• AND REPEAT