Experiments

• why are experiments carried out?

  to discover whether one factor affects another
• independent variable

  the thing that *I* change
• dependent variable

  the thing that is measured
• control variable


  the thing kept the same throughout
• extraneous variables 


  other variables that could potentially influence the DV apart from the IV
• experimental condition


  the condition which experiences change or manipulation
• controlled condition


  the condition which has not experienced the change or manipulation, to generate baseline results for those from the experimental condition to be compared against
• laboratory experiment


  the IV is manipulated by the researcher and the experiment is carried out in a laboratory or other contrived setting away from the participants' normal environment
• field experiment 


  the IV is manipulated by the researcher but this time the experiment is carried out using participants in their normal surroundings
• quasi-experiment


  the IV is naturally occurring, not manipulated by the researcher
• advantages of lab experiments

  the control in a laboratory experiment will produce scientific research which ensures that the IV is the only thing affecting behaviour
• disadvantage of lab experiments

  less ecological validity as the setting is artificial and so does not reflect real life
• advantage of field experiments

  offer a more realistic setting, increasing ecological validity
• disadvantage of field experiment

  the lack of control can mean it is difficult to assume that the IV actually caused the behaviour
• advantage of quasi experiment

  allows us to study the effects that the variables which psychologists cannot change have on behaviour
• disadvantage of quasi experiment

  there is no control of social settings, lifestyle and how they were brought up
• repeated measures design


  this involves using the same people in each condition
• independent measures design 


  this involves using different people in each condition
• matched participants design

  this involves using different people in each condition but an attempt is made to make the participants as similar as possible based on certain characteristics that may influence findings. this is done by testing the individuals on the key characteristics, pairing them and then placing one member of each pair into each group
• advantage of repeated measures design


  the best design for controlling subject variables

  often uses fewer participants so could be more cost and time effective
• disadvantages of repeated measures design

  requires a counter balance as practice, fatigue and boredom could affect results

  it is easier for participants to work out the aim of the experiment and use demand characteristic, lowering the validity of the results
• advantage of independent measures design

  not affected by practice, boredom and fatigue

  less likely to be affected by demand characteristics

  less time consuming than matched participants design
• disadvantages of independent measures design

  does not control extraneous variable effectively

  large samples are often needed ignorer to be sure that any affect of the IV is caused by the Dv not individual differences
• advantages of matched participants design

  unlikely to be affected by practice, boredom and fatigue

  less likely to be affected by demand characteristics

  controls the participant variables better than independent measures
• disadvantages of matched participants design

  very time consuming and so is not often used

  impossible to match participants enough to make sure there are no extraneous variables
• participant variables


  are characteristics of the individual participant that may influence the results

  eg. age, intelligence, skill, experience, gender
• how to control for participant variables

  either have the same people in each condition or extremely similar people in each condition

  if using independent groups design, make a point of allocating participants to conditions on a random basis
• situational variables


  any feature of the research situation which may influence a participant's behaviour an therefore the result

  eg. order effects- when doing the same activity twice, participants may do better the second time because of practice or worse because of boredom
• how to control for situational variables

  having different people in each condition will avoid this problem

  if a repeated measures design is used, then this should be counter balanced
• how to control for environmental factors (such as time of day, temperature and noise)


  impose controls on the experiment to ensure that there are as few differences as possible between the two conditions
• demand characteristics


  cues in an experiment that communicate to participants what is expected of them and which may unconsciously affect the behaviour of participants
• how to control for demand characteristics

  do not tell participants the aim of the investigation (a single blind procedure)
• researcher effects

  results affected by researchers behaviour during the experiment
• researcher bias


  results affected by researchers behaviour after the experiment
• an alternative hypothesis


  this predicts how one variable is likely to affect another variable
• a null hypothesis

  predicts that the IV will not have an effect on the DV. any difference will be due to chance factors rather than the IV
• two tailed hypothesis


  predicts that the IV will have a significant effect on the DV, but it does not predict the direction this effect will go in
• one tailed hypothesis


  predicts not only that the IV will have a significant effect on theDV but also the direction this effect will go in (A will be better that B)
• self-selecting sample


  when people volunteer to take part in the study
• strengths of a self selecting sample

  access to a wide variety of participants and so representative