1.1.3 Experimentation

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Learning objectives

Can you state about eight principles of experimentation?

Planning & Design

Safety Procedure

Control Experiment

Sample Size

Random Selection

Replicaton

Double-Blind Testing

Sources of errors

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What is an experiment?

1. An experiment is a controlled test.

2. Only one variable should be changed at a time.

a. Independent variable – changed by the experimenter.

(Hint: I change the Independent variable) b. Dependent variable (Responding) – the

effect.

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3. Constants do not change.

4. Controlled variables are those which could change, but are not allowed to.

5. Two parts to an experiment:

a. Control group – normal conditions.

b. Experimental group(s) – variables are changed.

6. Prediction is the goal of experiments.

What is an experiment?

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How to organise an experiment OR

The Principles of Experimentation

1. Plan and design the experiment

2. Be aware of Safety procedures

3. Select organisms at random

4. Use a large enough sample size

5. Use a control group

6. Use Double-blind testing

7. Change one factor at a time

8. Measure changes 9. Analyze the results10. State possible

sources of error11. Repeat the

experiment

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Learning check

What is an experiment?

• It is a controlled test where only one variable is changed at a time.

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An example of an experiment

Observation: It has been suggested that large daily doses of Vitamin C protect against the common cold virus.

Hypothesis: Vitamin C protects against the common cold virus

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An example of an experiment

Experiment design: Ten adult males in their mid twenties who are friends of the investigator were chosen to test the possible value of vitamin C.

5 of them were given 3000mg of vitamin C a day; the other 5 were given a placebo.

Which is the control group?

Which is the experimental group?

Is this a good experiment?

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Problems with experiment design

All males

All mid twenties

All friends

Not a large enough sample

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A Good Experiment

Should

• Have only one variable

• Use a large number of samples

• Use random selection

• Be repeated

• Use double blind testing

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Learning objectives

Can you state about eight principles of experimentation?

Planning & Design

Safety Procedure

Control Experiment

Sample Size

Random Selection

Replicaton

Double-Blind Testing

Sources of errors

12

ENDThanks to the PDST biology support team for the excellent

2011 resources DVD