Experimental designs

• Key Characteristics of Independent groups is that the participants are spilt across the independent variables conditions and equal amounts assigned to each condition.
• Key characteristics of a repeated measures is that all participants take part in the independent variable condition/s and also same technique is followed in the two or more than two conditions. However ppts go in different orders to cancel order effects out.
• Key characteristics of matched pairs is that parcipants are paired on characteristics that could effect the dependent variable and also then the pairs are put into separate conditions to draw comparisons between differing independent variables.
• Advantages of Independent groups: no order effects (time and effort saved as both conditions can be tested simultaneous, also same stimulus material across all conditions of the independent variable of task changing difficulty) also more attrition as not a huge loss of data if one person drops out.
• Advantages for repeated measures: uses fewer participants, saves money and time and effort. Also removes participant variables as person is participating in all conditions.
• Advantages of matched pairs: good control over participants, also eliminates order effects reducing impacts of participant variables (likely to be skewed is similar people in same conditions). Also only exposed to one independent variable meaning behaviour is more natural (ecological validity).
• Disadvantages of Independent groups: participant variables may effect the results (may differ in a crucial way) also twice as many participants needed as only doing one condition
• Disadvantages of repeated measures: risk of order effects, also a risk that participants will figure out the experiments aim which decreases ecological value.
• Disadvantages of matched pairs: matching participants can be a challenge, it is time consuming and also less participation attrition (1 person gone= 2 pieces of data)
• Best circumstance to use Independent groups when: larger number of participants wanted, stimuli needs to be kept the same across the conditions to avoid skewing the dependent variable. Also if you want less confounding variables as they are less likely given the nature of the research question.
• Best circumstance to use repeated measures: small numbers of participants, if participant variables would highly (likely to) effect the results of what you are studying. Also if the stimulus materials do not need to be kept the same across conditions to avoid skewing the dependent variable. Also participants aren’t likely to work out the research question (ecologically valid)
• Best circumstances to use Matched pairs in: larger number of participants available, also if participant variables would highly skew the results of the study if you had people with very different characteristics in each condition.
• With random allocation it reduces the possibility that people with similar characteristics will be placed in the same conditions
• Randomisation reduces ‘selection bias’ affected by unconscious manipulation of the grouping of the study and can also effect how the researchers assign the stimulus- unintentionally manipulating outcome of experiment by making IV harder/ different for some
• Standardisation is when you make the experiment conform to the standard- meaning that it is a controlled experiment that eliminates the order effect
• Counterbalancing participants will cancel out any order effects due to them experiencing boredom at different times meaning the impact the IV is having is actually due to the IV (go through the experiment opposite ways)