experimental methods

• extraneous variables are variables that may make it more difficult to detect an effect
• confounding variables is a change systematically with the independent variable so we cannot be sure if any observed change in the dependent variable is due to the control variable or the independent variable
• demand characteristics refer to any cue from the researcher or research situation that may reveal the aim of the study and change participants' behaviour
• investigator effects are any effects of the investigators behaviour on the outcome of the research (dependent variable) and also on design decisions
• randomisation is the use of chance when designing investigations to control for the effects of bias
• standardisation is using exactly the same formalised procedures for the all participants in a research study
• pilot studies are small scale trail run of an investigation to 'road-test' procedures, so that research design can be modified. Control groups/conditions are used to set comparison and act as a baseline to help establish causation
• single-blind experiment is when a participant doesn't know the aims of the study so that demand characteristics are reduced
• double-blind experiments are when both the participant and researcher don't know the aims of the study to reduce demand characteristics and investigator effects
• independent groups is when one group does condition a and a second group does condition B. Participants should be randomly allocated to experimental groups
• strengths of independent groups:

  • no order effects- participants are only tested once so can't practise or become bored/tired. This controls an important control variable
  • will not guess aim- participants only tested once so are unlikely to guess the research aims. Therefore behaviour may be more 'natural' (higher realism)
• limitations of independent groups:

  • participant variables- the participants in the 2 groups are different. This may reduce the validity of the study
  • less economical- need twice as many participants as repeated measure for some data. More time spent recruiting which is expensive
• repeated measures is when the same participants take part in all conditions of an experiment. The order of conditions should be counterbalanced to avoid order effects
• strengths of repeated measures:

  • participant variables- the person in both conditions has the same characteristics. This controls an important control variables
  • fewer participants- half the number of participates is needed than in independent groups. Less time spent recruiting participants
• limitations of research measures:

  • order effects are a problem- participants may do better or worse when doing a similar task twice. This reduces the validity if the results
  • participants guess aims- participants may change their behaviour. This may reduce the validity of the results
• matched pairs are when 2 group or participants are used but they are also related to each other by being paired on participant variables that matter for the experimenter
• strengths of matched pairs:

  • participant variables- participants matched on a variable that is relevant to the experiment. This controls participant variables and enhances the validity of the results
  • no order effects- participants are only tested once so no practice or fatigue effects. This enhances the validity of the results
• limitations of matched pairs:

  • matched is not perfect- matching is time consuming and can't control all relevant variables. Cannot address all participant variables
  • more participants- need twice as many participants as repeated measures for same data. More time spent recruiting which is expensive