The Statistics Involved in Experiments
Carl Hamblyn
SO_P
S_AR
Designing an Experiment
• An experiment is a set of observations made under conditioned controlled by the observer
• Experiments allow us to claim cause and effect (if correctly designed)
Components of Experiment
• Question• Variables• Design
• Replication• Blocking• Randomisation
Question
• Question• Variables• Design
• Replication• Blocking• Randomisation
• “The purpose of this experiment is to see if…
• … has an effect on…”
• E.g. “The purpose of this experiment is to see if adding nitrate solution has an effect on the yield of tomatoes at harvest time.
Question (try to be precise)
Variables
• Question• Variables• Design
• Replication• Blocking• Randomisation
Independent and Dependent
• Independent – the treatment• Dependent – the one you measure
Replication
• Question• Variables• Design
• Replication• Blocking• Randomisation
Not just once…
Components of Experiment
• Question• Variables• Design
• Replication• Blocking• Randomisation
Blocking (homogeneous groups)
Randomisation
• Question• Variables• Design
• Replication• Blocking• Randomisation
Experiment Group and
Control Group
Random allocation is important
Year 12 vs Year 13
• Comparison between two groups– need a control group. – need an experimental group
• Comparison within the same group– before and after. – with the treatment, without the treatment
Ideas and help
• BBC website (google BBC psychology test)• Census at School website
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