experimental design

• experimental design refers to the way in which participants are used in experiments
• an independants group design is when two seperate groups of participants experience two different conditions of the experiement. all participants experience one level of the IV only. one half may experience the experimental condition and the other may experience the control condition. the performance of the two groups are then compared.
• one limitation of indepedent groups is that the participants who occupy the different groups are not the same. if the researcher finds a mean difference between the groups on the DV this may be more to do with individual difference (participant variables). to deal with this, participants may use random allocation. another limitation is that they are less economical than repeated measures as each participant contributes a single result only. twice as many participants would be needed to produce equivlant data to that collected in repeated measures
• a strength of independent groups design is that order effects are not a problem whereas they are a problem for repeated measures designs. participants are less likey to predict the aims as they only experience one condition
• repeated measures is when participants experience both the experimental condition and the control condition. after, the two sets of data from both conditions would be compared to see if there was a difference. this garuantees that we are comparing 'like with like'.
• counterbalancing is used in repeated measures design as an attempt to control for the effects of order in a repeated measures design. half the participants experience the conditions in one order and the other half in the opposite order
• one issue with repeated measures is order effects as the task may cause problems like fatigue that cause deterioration in performance on the second task so it matters what order they are in. order is a confounding variable. in this scenario, counterbalancing may be used to minimise this. another issue is that participants may find the true aim of the study which may result in demand characteristics
• in a matched pairs design, participants are paired up based on some characteristic such as age or gender. the pairings are made so that the characteristics are similar within each pair but differ across pairs. the two members of each pair will then take part in either the experimental or control condition.
• a strength of repeated measures is that participants variables are controlled and there are fewer participants needed
• in a matched pairs design, participants are paired together on a variable that is relevant to the experiement. this may include IQ if doing a memory experiment. the two participants with the first and second highest IQ scores would be paired together. then one participant from each pair would be allocated to a different condition of the experiment. this controls confounding variables of participants.
• one strength of matched pairs design is that participants only take part in a single condition so order effects and demand characterisitics are less of an issue.
• an issue with matched pairs is that participants cannot be matched exactly as there will still be some important differences that affect the DV. also, matching may be time consuming and expensive especially if a pre test is required so this is less economical