Experimental design - RM

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  • Experimental Research Methods
    • Types of experiments
      • Lab
        • Conducted in a well controlled environment, where accurate measurements are possible. 
          • Strength: They allow for precise control of extraneous and independent variables. This allows a cause and effect relationship to be established. 
          • Limitation: The artificiality of the setting may produce unnatural behavior that does not reflect real life, i.e. low ecological validity. This means it would not be possible to generalize the findings to a real life setting.    
      • Field
        • done in the everyday (i.e. real life) environment of the participants. The experimenter still manipulates the independent variable, but in a real-life setting (so cannot really control extraneous variables). 
          • Strength: There is less likelihood of demand characteristics affecting the results, as participants may not know they are being studied. This occurs when the study is covert. 
          • Limitation: There is less control over extraneous variables that might bias the results. This makes it difficult for another researcher to replicate the study in exactly the same way. 
      • Natural
        • Natural experiments are conducted in the everyday (real life) environment of the participants, but here the experimenter has no control over the IV (it's naturally occurring)
          • Strength: Behavior in a natural experiment is more likely to reflect real life because of its natural setting, i.e. very high ecological validity.
          • Limitation: There is no control over extraneous variables that might bias the results. This makes it difficult for another researcher to replicate the study in exactly the same way. 
    • Controlled experiment
      • Controlled experiment - when a hypothesis is scientifically tested. In a controlled experiment, an independent variable (the cause) is systematically manipulated and the dependent variable (the effect) is measured; any extraneous variables are controlled.
      • Control group
        • not exposed to the independent variable under investigation and so provides a base line against which any changes in the experimental group can be compared.
      • Extraneous variable
        • all the other variables that could affect the dependent variable    
      • Why do psychologists conduct controlled experiments?
        • they allow for precise control of extraneous and independent variables. This allows a cause and effect relationship to be established.
        • Controlled experiments also follow a standardised step by step procedure. This makes it easy another researcher to replicate the study.
    • Experimental design
      • What is experimental design?
        • refers to how participants are allocated to the different conditions (or IV levels) in an experiment.
      • Independent measures
        • Different participants are used in each condition of the independent variable.  This means that each condition of the experiment includes a different group of participants. 
          • Weakness: More people are needed than with the repeated measures design (more time consuming).
          • Strength: Avoids order effects (practice or fatigue) as people participate in one condition only.  If a person is involved in several conditions, they may become bored, tired and fed up by the time they come to the second condition, or realise aims of experiment 
      • Repeated measures
        • same participants take part in each condition of the independent variable.    
          • Strength: participant variables reduced - individual differences
          • Order effects  (order of the conditions have an effect on the participants’ behaviour).  Performance in condition 2 may be better because the participants know what to do (practice effect). Or their performance might be worse  due to tiredness (fatigue effect). 
      • Matched pairs
        • different participants used in each condition, but are matched on key characteristics
          • Strength: reduces participantvariables and avoids order effects (counterbalancing not necessary)
          • Weakness:  Very time-consuming trying to find closely matched pairs.    
    • Indepedant and dependant variables
      • Indépendant variable
        • the variable the experimenter changes or controls and is assumed to have a direct effect on the dependent variable.
      • Dependant variable
        • the variable being tested and measured in an experiment, and is 'dependent' on the independent variable.
    • Extraneous variables
      • all variables, which are not the independent variable, but could affect the results of the experiment.
      • Types of extraneous variables
        • Situational Variables    
          • aspects of the environment that might affect the participant’s behaviour, e.g. noise, temperature, lighting conditions    
        • Participant variables
          • the ways in which each participant varies from the other    
        • Investigator Effects
          • experimenter unconsciously conveys to participants how they should behave 
        • Demand Characteristics    
          • all the clues in an experiment which convey to the participant the purpose of the research   

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