Chapter 1 Principles of Experimentation

1.1.3 Experimentation Syllabus requirements A full understanding of the principle of experimentation to include Careful planning and design Safety of procedure Necessity and selection of an experimental control Explaining why sample size is important Explaining why random selection is important Explaining why replicates are important Explaining why double - blind testing is important

Principles of experimentation This is not a fair test because…

This is not a fair test because: They will run on different surfaces They are wearing different shoes They are wearing different clothes One is carrying a bag Etc.

How to organise an experiment OR The Principles of Experimentation Plan and design the experiment Be aware of Safety procedures Select organisms at random Use a large enough sample size Use a control group Use Double-blind testing Change one factor at a time Measure changes Analyze the results State possible sources of error Repeat the experiment

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.

What is an experiment? 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 double-blind testing? During trials to examine the effectiveness of a new pill, two sample groups are taken. One group gets the pill under test and the other a placebo. All pills are the same size, colour, taste, etc., but coded differently. When the trials are over, it is possible to distinguish between the control and experimental groups. This ‘double-blind’ testing method avoids bias during the trials.

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

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?

Problems with experiment design All males All mid twenties All friends Not a large enough sample

A Good Experiment Should Have only one variable Use a large number of samples Use random selection Be repeated Use double blind testing

Revision Questions Experimentation

A hypothesis confirmed by experiment Fill in the table Key Word Explanation Variable A hypothesis confirmed by experiment Scientific Method Control An “educated guess”

Completed table Key Word Explanation Variable Any condition which changes during the experiment Theory A hypothesis confirmed by experiment Scientific Method A process of investigation Control A comparison Hypothesis An “educated guess”

QUESTION: Explain Independent variable The variable that is changed by the person doing the experiment. Remember: If I am doing the experiment then I change the Independent variable

QUESTION: Explain Dependent variable This is what changes in response to the changing of the independent variable.

QUESTION: What is a control or control group? Experiment(s) that are subjected to normal conditions. You usually know how these are going to react.

Learning objectives Can you state about eight principles of experimentation? 5. Random Selection 6. Replication 7. Double-Blind Testing 8. Sources of errors Planning & Design Safety Procedure Control Experiment Sample Size

How would you organise an experiment? Plan and design the experiment Be aware of Safety procedures Select organisms at random Use a large enough sample size Use a control group Use Double-blind testing Change one factor at a time Measure changes Analyze the results State possible sources of error Repeat the experiment

Limitations of the Scientific Method

Is limited by the extent of our basic knowledge is limited to what can be observed with the five senses tells us “how” a process works, not “why” e.g., does not really explain why the Universe exists may be affected by the emotional involvement of investigator may be affected by time pressure for results

limitations of our measurement instruments ethical and legal responsibilities religious beliefs we can never be sure all untested variables are controlled scientists sometimes make mistakes

Song on Scientific Method

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