Experimental design

    Cards (12)

    • Experimental design= the method you use to allocate your pps to complete conditions within your study
    • Repeated measures:
      • All pps are tested in each of the IV conditions & results from each condition are compared
      • Can lead to order effects from the pps (changes in performance because both tasks are being carried out)
      • PPs may guess the aim of the study- demand characteristics
      • Don't need to recruit as many pps- minimised participant variables
    • Independent groups:
      • PPs are divided into 2 groups & tested on one condition, results from each group are then compared
      • You need twice as many pps- more costly & time-consuming for the researcher
      • No order effects & less likely to be demand characteristics
      • PP effects: they are different pps so you have no control over natural variations between participants (one group could be more intelligent than the other)
    • Matched pairs design:
      • Recruit one group of pps and then get pps who match them on relevant characteristics. Each group tested in 1 condition & compare results (twins are ideal pps; they're already matched)
      • Very time-consuming (need to find lots of matching pps)
      • Can rarely find exact matches & can never be sure you have matched all the relevant variables.
    • Most scientific experiments meet the criteria of:
      • researcher manipulates the IV
      • researcher randomly assigns pps to conditions
      • researcher has control over extraneous variables
      Having these features allows you to establish cause & effect.
    • Laboratory experiment:
      • Experiment conducted in a specific environment, where variables can be carefully controlled.
      • Involves manipulation of an IV & measurement of DV- therefore enables us to establish cause & effect
      • High level of control of extraneous variables
      • PPs randomly allocated
      • Artificial setting so reduces ecological validity
      • Higher chance of demand characteristics
      • IV manipulated by researcher- systematic & replicable so more likely to produce reliable results.
    • Field experiment:
      • Conducted in a more natural environment & IV manipulated by researcher.
      • Higher levels of ecological validity & reduced demand characteristics.
      • Involves manipulation of IV & measurement of DV- therefore enables us to establish cause & effect.
      • Cannot control all EVs to same extent as lab.
      • PPs are not necessarily randomly allocated.
    • Natural experiment:
      • Changes in the IV are natural rather than manipulated by the researcher, as it would be unethical or impractical to set conditions.
      • Can be higher in ecological validity if in natural environment
      • No random allocation
      • Difficult to replicate- may have low reliability
      • Not all extraneous variables are controlled
      • Not a 'true' experiment due to lack of manipulation of an IV & so cannot therefore state cause & effect.
      • Can allow for research that otherwise couldn't take place.
    • Quasi experiment:
      • The IV is not manipulated by the researcher as it has naturally occurring differences between people.
      • Can allow research into individual differences
      • Low control of extraneous variables
      • Cannot randomly allocate pps
      • Not a 'true' experiment due to lack of manipulation of an IV & so cannot therefore state cause & effect.
    • The purpose of experiments is to compare the difference(s) between 2 variables.
    • A pilot study= a small scale version of your main study (fewer pps & cheaper resources).
    • Pilot studies are used as a trial for all aspects of the method so that improvements can be made & they help to test the validity & reliability of the method selected- to help you identify any potential flaws.
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