experimental designs

• Independent groups:

  • Separate groups of people for different levels of the IV - conditions.
  • a control and experimental group
• Strength of Independent groups:

  • No order effects (e.g. practice effect) as participants will only do task once sp wont benefit from practice
  • Participants less likely to guess study aims – lower risk of demand characteristics.
• Weakness of Independent groups:

  • Participant variables can influence results and act as an EV. This reduces validity of the results
  • Double the amount of participants required for each condition
• Dealing woth participant variables (independent groups)

  • RANDOM ALLOCATION- random way of allocating partcipants to the conditions
• Repeated Measures:

  • The same group of people take part in both conditions
  • Usually experimental and control condition
• Strengths of repeated measures:

  • No participant variables as the same people are being used. Each participant is being compared to themselves rather than other people. Increases validity of results
  • Fewer participants needed- less expensive
• Weakness of repeated measures:

  • Higher chance of order effects – e.g. practice effect- as particpants are tested twice. Order in which they do the tasks may make a difference. Affects validity of results
  • May be easier for participants to guess the aims of experiment – demand characteristics
• Dealing with order effects (repeated measures)

  • COUNTERBALANCING- half the participants complete the conditions in one order, the other half in the opposite order
• Matched pairs:

  • Particpants paired on relevant variables
  • Separate groups of people take part in different conditions but are matched up based on key participant variables
  • each pair goes in each group
• Strengths of matched pairs:

  • No order effects – participant only does study once
  • Fewer participant variables - matching shared characteristics
  • those taking part are matched on an important variables- this increases validity of results
• Weakness of matched pairs:

  • Time consuming to match participants
  • Not all participant variables eliminated so may not be worthwhile
• Why can participant variables be an issue?

  • May influence the results for each group
  • Can be an issue when comparing the results of the experimental group to the control group
  • Lack of validity