The Experimental Method

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  • Created by: Erin
  • Created on: 16-05-13 16:42

What is involved in an experiment?

Independant Variable = the thing you manipulate

Dependant Variable = the thing you measure

Experimental Hypothesis = what you think will happen

Null Hypothesis - what you think will not happen

Controlled Variable = the thing you try to keep the same - less extraneous variables which means it is easier to measure cause and effect

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Key feautures of the Experimental Method

Theory = the aim of an experimental is to test a hypothesis with the aim of disproving or supporting

Test = one variable has to have a measurabl effect on the other variable

Control = the environment must be controlled so that the experiment is due to the identified variable and not due to random factors (casue and effect)

Replication = for a theory to be supported i much be able to be repeated by others. This requires a precise aqnd standard method

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Steps in an experiment

1) Experimenter comes up with a hypothesis

2) The experimenter designs an experiment to test

3) One factor is manipulated (IV)

4) The effect is measures due to the manipulation (DV)

5) Other variables are controlled

6) The experimenter analyses the mean in each group (condition)

7) If there is a significant difference between the means, the H1 (experimental hypothesis) is supported

8) If there is no significant different between the means, the H0 (null hypothesis) is supported

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Controlling the variables

  • Running an experiment looks at the effect of the IV on the DV
  • However, certain factors can affect the reults
  • These are Extraneous or Confounding variables
  • There are many ways to control these variables, these are individual to each study

EXAMPLE: The prupose of the study is to understand how the use of different verbs affects the estimations of the speed of a car. to this this they showed a video clip of an accident and asked a question using different varibles

IV: verb used

DV: estimation of speed

Controls: the video shown, time of day. the question, age of ppts, how long they've been driving

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Controlling the variables (2)

Confounding variables dramatically reduce the reliability and validity of the study


When the results are close together & similar everytime the experiment is releated. You could be at risk of anomolous reults or outliers


When you measure what you intend to and meet the aim. Confounding variables could change what you are trying to measure which makes them less valid

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Laboratory Vs Field

  • Lab and Field experiments two examples of experimental methods


  • Field experiments are public. Participants are not controlled


  • Lab experiments have controlled IV, DV, participants and task variables
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Evaluating Lab methods


  • Tighter control of variables
  • Easier to comment on cause ad effect
  • Relatively easy to replicate
  • Enable use of complex equipment
  • Often cheaper and less time-consuming than other methods


  • Demand characteristics - ppts aware of experiment, may change behaviour
  • Atrificial environment - low realisn
  • May have low ecological validity - difficult to generalise to other situations
  • Experimenter effects - bias when experimenter's expectations affect behaviour
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Evaluating Field methods

Field experimennt takes place anywhere in a natural setting e.g. shopping centre, train, supermarket.

A field experiment is an experiment where the IV is not manipulated. Not all field studies are experiments.


  • People may behave more naturally than in a laboratory - higher realism
  • Easier to generalise from results


  • Often only weak control of extraneous variables - difficualt to replicate
  • Can be time-consuming and costly
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Quasi Experiments

Quasi experiments are normally classes as such, when an experimenter has not manipulated the IV...

Instead there are normally two groups with a difference - natural difference e.g. gender or age

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Evaluating Quasi research


  • High ecological validity (in principle) die to natural setting
  • Used in a wide variety of environments (crime, health, sport)
  • Radon participants delection (increases usefulness)
  • No bias increases the validity due to more accuracy


  • Little to no control of confounding variables - validity
  • Unable to work out cause and effect
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