Lesson 7 - Experimental designs Flashcards
(10 cards)
Types of experimental design
Repeated measures
Independent groups
Matched pairs
Randomisation
The use of chance in order to control the effects of bias from investigator effects.
This can be done for:
- the design of the materials, such as the order of a list of words
- deciding the order of conditions
- selecting participants.
Standardisation
Using exactly the same formalised methods and instructions for all participants. This improves the reliability of the study as it can be repeated exactly the same.
Random allocation
An attempt to control for participant variables in an independent measures design which ensures that each participant has the same chance of being in one condition or the other.
Strengths of independent groups
Order effects will not occur because there are different participants in each condition.
Less chance of guessing the aims of the studies, so demand characteristics are less likely
Weaknesses of independent groups
More participants are needed for independent measures compared to repeated measures. If you have 10 participants for a condition, you will need 20 different participants.
Different results gained between condition A and B may be due to participant variables like individual differences rather than the IV. Weakens validity of the results. Can be fixed with random allocation.
Strengths of repeated measures
No individual differences as all participant is tested in both conditions. We can be more sure that the results are the effect of the IV and not participant variables. Higher validity
If you have 10 participants for a condition, you only need 10 participants. You need less people for a study compared to independent measures designs.
Disadvantages of repeated measures
Order effects may affect the results. Needs to be removed through counterbalancing
Demand characteristics are more likely to occur because participants have more opportunities to guess the aim of the study. This may affect their behaviour and the data will be invalid.
Strengths of a matched pairs design
Less risk of order effects as participants are only taking part in one condition only unlike a repeated measures design.
Individual differences are lessened/minimised, because pps are matched closely on a specific characteristic, like age or gender
Weaknesses of matched pairs
You still need twice as many pps for the study. Therefore you will need to gain access to many participants.
May be difficult and time consuming.
Even those with matched characteristics may feel different levels of fatigue, motivation etc. Therefore differences cannot be fully controlled with this.
