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Practical Investigations

Practical Investigations. Activity c – Investigating the difference between two conditions i.e., An experiment. Experimental Design. In an experiment we manipulate an IV There are usually two values of the IV e.g. Doing homework with background noise or doing it with no noise

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Practical Investigations

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  1. Practical Investigations • Activity c – Investigating the difference between two conditions • i.e., An experiment

  2. Experimental Design • In an experiment we manipulate an IV • There are usually two values of the IV e.g. • Doing homework with background noise or doing it with no noise • Deep or shallow processing • These determine the conditionsof the experiment • The conditions can be arranged different ways according to the design of experiment

  3. Experimental Design • 3 main types • Independent measures • Repeated measures • Matched participants

  4. Compare the results for the two groups Independent Measures Recruit a group of participants Divide them into two This group does the experimental task with the IV set for condition 1 This group does the experimental task with the IV set for condition 2 Measure the DV for each group

  5. Compare the results for the two conditions Repeated Measures Recruit a group of participants Condition 1 Condition 2 The group does the experimental task with the IV set for condition 1 The group repeats the experimental task with the IV set for condition 2

  6. Compare the results for the matched pairs Matched Participants Recruit a group of participants Find out what sorts of people you have in the group Recruit another group that matches them one for one Treat the experiment as independent measures Condition 1 Condition 2

  7. Problems with Independent Measures Design • Participant Variables – chance variation between participants can affect DV • E.G, in a test of a sample population’s mathematical ability, all participants in group 1 just happen to have a maths degree. In group 2, all participants happen to all be really bad at maths . • Could imply an effect where none exists (false positive) • Control by random assignment to groups • Use repeated measures or matched PPs instead

  8. Problems with Repeated Measures Design • Carrying out a task repeatedly leads to changes in performance • Deterioration as PPs become tired or bored • Improvement due to practice • Solutions • Leave a long gap between conditions • Counterbalanced design • Use independent measures or matched participants

  9. Counterbalancing • Important control when using repeated measures • Reduces ‘carry over’ effects • Half PPs do condition A then B • Other half do condition B then A • Fully counterbalanced: ABBA

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