Experimental Designs

Nota:

• Strengths - Green Limitations - Red

1. Indepent Measures Design

   Nota:

   • Has two or more conditions woth different participants in each condition.
   1. Participants only have to do the task once and are less likely to become bored or to work out why/what they are being tested on is less likely to be obvious to them.
   2. The same task can be used for each group - Higher chance of controlling the independent variables.
   3. Avoids order affected

      Nota:

      • This is called counter-balancing.
   4. Non-equivalence of samples due to the different conditions.

      Nota:

      • Short version - Individual differences
   5. You would need to get twice as many participants as you would for a repeated measures experiment and where there is too great a difference between the statistical variances of independent groups may be be able to proceed with parametric tests.
2. Repeated Measures Design

   Nota:

   • The same participants are used in each condition.
   1. Participants are the same and are therefore easier to compare each conditions performance.
   2. You need fewer participants as they will take part in each condition.
   3. Is more convenient and time saving than other designs as more data can be gathered as everybody does each of the task.
   4. Practise effects (essentially order effects) - Participants may improve with each task as they are practising what they are doing.
   5. There is the possibility of order effects which would result in fatigue effects as the partipants may get tired after doing a certain amount of tasks.

      Nota:

      • Order effects - Where the participant is able to practise, and therefore gain experience due to the repition of the tasks. This changes their initaial knowledge of how they would complete the tasks, decreasing the validity of the results.
   6. Demand Characteristics - There is a higher chance of participants figuring out what they are being tested on/the aim of the study and start acting accordingly to what they beilieve the researchers want te results to be.
3. Matched Pairs Design

   Nota:

   • A participant in one condition is matched with a particpant in every other condition as close as possible. This is done as closely as possible via age, race, gender, background, ect.
   1. Participants only have to be tested once.
   2. Differences between the two groups are reduced, results ae therefore more valid.

      Nota:

      • (More valid results)
   3. Helps decrease problems such as individual differences and order effects.

      Nota:

      • Extranuous variables - A variable that has occured outside the tudy and may effect the results. Confounding Variable - A variable that occurs inside the study that may have effected the results.
   4. Good attempt at controlling the participant variables and the differences they could cause, allowing the sample to be representative.
   5. Lengthy and time consuming process that can be quite 'wasteful' of participants as a large number of people need to be tested to find appropriate pairs.
   6. Difficult to match participants exactly.
   7. More participants are needed.