1. 1.1.3 Experimentation

2. 2 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

3. 3 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.

4. 4 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?

5. 5 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 results 10.State possible sources of error 11.Repeat the experiment

6. 6 Learning check What is an experiment? It is a controlled test where only one variable is changed at a time.

7. 7 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

8. 8 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?

9. 9 Problems with experiment design All males All mid twenties All friends Not a large enough sample

10. 10 A Good Experiment Should Have only one variable Use a large number of samples Use random selection Be repeated Use double blind testing

11. 11 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. 12 END Thanks to the PDST biology support team for the excellent 2011 resources DVD