Experimental designs Flashcards
What are experimental designs?
-Experimental designs refers to how the participant sample is used in combination with the different levels of the IV
What are the three main types of experimental designs?
-Independent group designs
-repeated measure designs
-Matched pairs design
What happens in independant group design?
-Participants only experience one condition of the IV
-Participants are randomly allocated to each condition to avoid researcher bias
-Independent groups design generates unrelated data (because the two groups are separate to one another)
-The performance of the group in condition 1 is compared to the performance of the group in condition 2,
What are strengths of the independent group design?
-Less likely to have demand characteristics as participants only take part in one condition, meaning they are less likely to guess the purpose of the study and how they behave for that purpose
-Less likely to be order effects because participants have only taken part in one study
What are limitations of the independent group designs?
-There can be participant variables/individual differences
-If more participants with a particular characteristic are assigned randomly to one condition, this can effect the results
-More participants are needed to ensure there are enough to take part, which can sometimes be problematic, if enough participants are not easy to find.
What is repeated measure design?
-participants experience all the conditions of the IV
What happens in a repeated measure design?
-Each of the participants complete each of the experimental conditions
-Repeated measures design generates related data
-Participants act as their own control group as their performance in condition 1 can be compared to their performance in condition 2,
How can you control order effects in repeated measure design?
Counterbalanced:
-Half of the participants experience condition 1 followed by condition 2
-The other half of the participants experience condition 2 followed by condition 1
What are strengths of repeated measure designs?
-There are no individual differences as the same participants are used in each condition, meaning participant variables do not affect the measurement of the IV
-Fewer participants are required as each participant generates two scores
What are the weaknesses of repeated measure designs?
-Order effect can be a problem as participants can take part in all conditions. This can result in the performance improving in the second(or third, forth etc…) condition due to practice or learning what is expected or it could result in worse performance as the participants could be bored or tired.
-Demand characteristics as the participants are more likely to guess the purpose of the research due to taking part in multiple conditions.
What is matched pairs design?
-Participants (usually) achieve just one score as they (usually) only take part in one condition
-Participants are assessed and matched on the characteristic(s) that are important for the particular research they are taking part in, e.g. age, ethnicity, gender etc.
Often MZ (Monozygotic/ identical) twins are used for this design as they create the perfect matched pair (one twin can be assigned the experimental condition and the other twin the control condition)
What happens in a matched pair design?
- matched participants are then randomly allocated to one condition each
As each participant is related to their pair this design produces related data
What are the strengths of matched pair designs?
-Less likely to be order effects because PT are only taking part in one of the conditions.
-Almost factors out individuals differences as confounding variables as reseaarchers have striven to find a match per participant
What are the limitations of matched pairs design?
-Matching is difficult as it often impossible to match all characteristics, especially when the unmatched characteristic could be important to the results of the research. Also, even well matched participants could have different levels of motivation in the study, affecting the outcome.
-More participants are need to ensure there are enough to take part in the different conditions.
-Matching participants is very difficult and time consuming.
