experimental design

what is experimental design?

the way in which participants are allocated into the different conditions within an experiment

what are the three types of experimental designs?

• independent measures

• repeated measures

• matched pairs

what are independent measures?

each group or condition experiences different conditions of the experiment

what are the strengths of independent measures?

• no order effects - participants only take part in one condition so no repetition

• less demand characteristics - only see one condition so less likely to guess true aim

what are the weaknesses of independent measures?

• harder to compare groups - participants in each group aren’t the same

• lower validity - individual differences and confounding variables are likely to have a bigger impact on results

what are repeated measures?

each group or condition experiences all conditions of the experiment

what are the strengths of repeated measures?

• easy to make comparisons - as same people are in each condition you compare people against themselves which dec individual differences, therefore increasing validity

• more cost and time effective - fewer participants needed for a large sample as all participants take part in all conditions

what are the weaknesses of repeated measures?

• order effects are a confounding variable - participants take part in all conditions so are more likely to be affected by previous conditions, this decreases validity

• demand characteristics - by taking part in multiple conditions participants are more likely to guess true aim of study and change behaviours

what are matched pairs?

• participants are paired together on a variable relevant to the experiment

• within each pair each participant is allocated to condition 1, and the other to condition 2

• often requires a pre-test to make matching effective

what is counterbalancing?

a technique used to deal with order effects when using a repeated measures design

how is counterbalancing done?

the participant sample is split in half, one half completes the two conditions and the other completes the conditions in the reverse order

what are the strength of matched pairs?

• no order effects - participants only take part in one condition

• less demand characteristics - participant only take part in one condition

what are the weakness of matched pairs?

• participants can never be matched exactly - there’ll always be individual differences present so confounding variables may be present

• matching may be time consuming and expensive - especially if a pre-test is required, causing it to be less economical than other designs