AO3 - Types of Experimental Designs

• One strength of independent groups design is that there will be no order effects as participants only take part in one condition so they will not get bored/fatigued or better at the task/have lasting effects from one condition to the next (AO2) unlike repeated measures design where participants take part in all conditions and could have order effects.
• Another strength of independent groups design is that they can be used when repeated measures design is inappropriate (e.g. quasi experiments when looking at gender differences) (AO2) as each condition needs different participants.
• One weakness of independent groups design is that individual differences may affect the DV as there are separate groups of participants in each condition e.g. some participants could have a better memory which wouldn't be suitable in a memory study (AO2) lowering the internal validity unlike repeated measures that uses the same group of individuals in all conditions to reduce the effect of individual differences.
• Another weakness of independent groups design is that more participants are needed as two different groups are required for the different conditions (AO2) unlike repeated measures where you use less participants as every participant takes part in all conditions.
• One strength of repeated measures design is that individual differences between participants in each condition are removed e.g. IQ as potential confounding variables, as the same participants take part in all conditions (AO2). Therefore, the researcher can be more sure that any changes in the DV are due to the IV and not any other variable increasing the internal validity of the research unlike IGD that will use different participants in different conditions so individual differences could affect the DV.
• Another strength of repeated measures design is that it requires fewer participants as the same participants take part in all conditions (AO2) unlike in an independent measures design as separate groups are needed for separate conditions.
• One weakness of repeated measures design is that order effects may occur when participants take part in more than one experimental condition they may perform worse in the second condition (due to boredom or fatigue) or better in the second condition (due to practice), or there may be lasting effects from condition 1 to condition 2 (AO2) lowering the internal validity unlike independent measures where participants only take part in one condition so cannot be susceptible to order effects.
• Another weakness of repeated measures design is that there are increased chances of demand characteristics as participants take part in all conditions. They may pick up on clues given off by the researcher as they spend much more time with them, or from the research situation , and change their natural behaviour to help or hinder the research (AO2) lowering the internal validity, unlike IGD where participants are less likely to pick up on clues as the only take part in one condition of the research
• One strength of matched pairs design is that it reduces individual differences between participants as it matches participants on variables important to the research, such as IQ/age/happiness. (AO2) Therefore, the researcher can be more sure that any changes in the DV are due to the IV and not any other variable. Unlike in an independent measures where separate participants are in separate conditions.
• Another strength of matched pairs design is that there will be no order effects as participants only take part in one condition so they will not get bored/fatigued or better at the task/have lasting effects from one condition to the next (AO2) unlike repeated measures design where participants take part in all conditions and could have order effects.
• One weakness of matched pairs design is that it is very time consuming to match up and find similar participants. (AO2) especially if a pre-test is needed to match participant on a certain characteristic. The psychologists would need a very large pool of people unlike repeated measures design where you use the same participants in all conditions.
• Another weakness of matched pairs design is that individual differences cannot be fully eliminated. Psychologists match participants on variables important for the research but are not able to match participants on all variables (AO2). Therefore this could question the validity of the matched-pairs design. Unlike RM where each condition will use the same participants therefore, individual differences will be eliminated.