Experimental Design

• why is experimental design used?

  researchers use their p's in diff ways in diff exp, depending on the situation.
• what is an independent group design?

  • p's only experience one condition of the IV.
  • p's are randomly allocated to each condition to avoid researcher bias.
  • performance of group 1 compared to performance group 2.
• what are the strengths of an independent group design?

  • less likely to have demand characteristics (p's only take part in one condition)- less likely to guess the study's purpose and how to behave for that purpose.
  • less likely to be order effects.
• what are order effects?

  occur when the sequence in which experimental conditions or questions are presented influences p's responses, potentially leading to inaccurate or misleading results.
• what are the disadvantages of an independent group design?

  • there can be p's variables/individual differences (can't be generalisable).
  • more p's needed to ensure there are enough to take part, can be difficult if p's aren't easy to find.
• what is a repeated measures design?

  • p's experience all conditions of the IV.
  • the same p's complete each of the experimental conditions.
  • p's act as their own control group, as their performance in condition 1 can be compared to their performance in condition 2.
• what are the strengths of a repeated measures design?

  • there are no individual differences (same p's in each condition), p's variables don't affect IV measurement.
  • fewer p's are required as each p' generates at least two scores.
• what are the weaknesses of a repeated measures design?

  • order effects- p's take part in all conditions. this can influence performance levels, i.e. p is more tired or bored.
  • demand characteristics are more likely (more likely to guess the purpose as they do multiple conditions).
• what is a matched pairs design?

  • p's randomly allocated to 1 condition each.
  • p's achieve just one score as they usually only take part in 1 condition.
  • p's are assessed & matched on the characteristic(s) that are important for the particular research they are taking part in, e.g. age, ethnicity, gender.
• what are the strengths of a matched pairs design?

  • p's in 1 condition = less likely to be order effects.
  • almost factors out the individual differences, researcher has matched p's so p' variables are controlled to an extent.
• what are the weaknesses of a matched pairs design?

  • difficult to match characteristics.
  • more p's needed (enough in each condition).
  • difficult & time consuming.
• what is counterbalancing?

  where 1/2 the p's experience condition 1 followed by condition 2. other 1/2 experience condition 2 followed by condition 1.
• what is random allocation?

  the allocation of p's to conditions in an exp.