Lesson 7 Experimental Designs Flashcards
Experimental designs
The experimental design of a study is how the participants are organized within the experiment
Three types of Experimental designs
Independent groups
Repeated measures
Matched Pairs
Experimental condition
This involves a group of people who are exposed to the independent variable e.g. chocolate or noise.
Control Condition
This group receives no treatment and are used as a base line level to compare results against e.g. the group that receive no chocolate (no treatment)
Randomisation
The use of chance in order to control for the effects of bias when deciding the order of conditions.
For example, to make sure that a list of words are not too easy or too hard, it is a good idea to put them in random order which can be done through a computer or manually. This is especially important if you are using a repeated measures design and the same participants are taking part in two different conditions.
Standardisation
Using exactly the same formalised procedures and instructions for all participants in a research study – this improves the reliability of the study (the ability to repeat the study again and get the same findings)
Random Allocation
An attempt to control for participant variables in an independent groups design which ensures that each participant has the same chance of being in one condition or the other
Independent Group Design
In this design, different participants are used in each of the conditions.
Therefore each group of participants are independent from one another.
Participants are usually randomly allocated to each condition to balance out any individual differences.
An example might be that we put 20 participants’ names in a hat. We draw out the first name and they will go into group 1, the second person goes into group 2, the third person goes to group 1 etc.
Advantages of Independent Groups Design
1) Order effects will not occur as there are different participants in each condition. Order effects are when the sequence in which participants take part in conditions influences their performance or behaviour. For example, in a memory test participants may get better with practice and perform better in the second condition compared to the first condition. Participants may also get tired or bored when being asked to take part in more than one condition.
2) The chance of demand characteristics is reduced as participants take part in only one condition each and so have less chance to guess the aim of the study which could affect their behaviour and the data collected.
3) Participants are not lost between conditions/trials because they only take part in one condition only and then leave the experiment/study. However in a repeated measures design where participants are used for two conditions, there is a higher risk of participants being lost between conditions.
Disadvantages of Independent Groups Design
1) More participants are needed for this experimental design compared to a repeated measures design. In an independent groups design there are usually 2 experimental conditions (or more) with different participants in each group
2) There is always a chance that the different results gained between the two conditions are due to individual differences rather than manipulation of the independent variable. This is because two separate groups of people are used and they might be very different.
Repeated Measures Design
In the repeated measures design each participant is tested in all conditions of the experiment. For example one group might be tested today to see what effect chocolate has on their mood. The same group of people are tested again next Friday to see the effect of chocolate on their mood.
Advantages of Repeated Measures Design
1) As the same people are used in all of the conditions, there are no individual differences between the conditions. Therefore the study is more valid as we are really only measuring the effect of the IV on the DV.
2) Half as many participants are needed in this design compared to an independent groups design. This is because one group of participants e.g. (20) are used in condition 1 and again in condition 2. However an independent groups design would need 20 participants in condition 1 and 20 participants for condition 2.
Disadvantages of Repeated Measures Design
1) Order effects may affect the results (see over the page). One way to avoid order effects is counterbalancing, this is when half the participants do condition A first and then condition B second and the other half of the participants do condition B first and condition A second. Changing the order of the tasks helps to reduce order effects and negative impacts on data collection.
2) Demand characteristics are more likely to occur using repeated measures design as participants are involved in the entire study and take part in two conditions. They might guess the aims of the study and therefore this might affect their behaviour and the data collected.
Matched Pairs Design
In the matched pairs design, different participants are used in all of the conditions, just as with the independent groups design.
However, participants in the two groups are matched on characteristics important for that study, such as age, gender, level of education etc. Identical twins are often used in matched pairs designs.
Advantages of Matched Pairs Design
1) There is less risk of order effects using a matched pairs design as participants only take part in one conditions only (compared to repeated measures design).
2) Individual differences are less likely to occur as the groups have been closely matched on specific characteristics (less likely to occur compared to independent groups design).
