types of experiment

• An experiment is a study that investigates cause and effect and compares the effect of an independent variable on a dependent variable in groups receiving different levels of the independent variable.
• A laboratory experiment is an experiment where the independent variable is manipulated in an artificial, controlled environment.
• A strength of laboratory experiments is that there is a high degree of control over extraneous variables meaning the experiment will have high internal validity. This means that laboratory experiments can establish a clear cause and effect relationship between the IV and the DV. However, the participants behaviour in the study doesn’t generalise to how they would behave in their normal, everyday life meaning laboratory experiments will have low ecological validity.
• A field experiment is where the independent variable is manipulated in a natural, everyday life setting
• A strength of field experiments is that they have high ecological validity as participants are observed in natural, everyday life settings. However, field experiments have low internal validity as extraneous variables are difficult to control. Subsequently, it is difficult to establish a cause and effect relationship.
• A quasi experiment is an experiment where the independent variable can’t be manipulated and randomly allocated to groups because it’s a personal characteristic of the participants.
• A strength of quasi experiments is that it is the only way to study the effect of an independent variable that is a fixed personal characteristic of participants. However, quasi experiments may lack internal validity making it harder to establish cause and effect and participants can’t be randomly allocated to groups, meaning that uncontrolled participant variables might act as confounding variables.
• A natural experiment is an experiment where the independent variable is an event that has already happened and the IV cannot be manipulated or randomly allocated. Natural experiments are used when it wouldn’t be practical or ethical to manipulate the IV.
• A strength of natural experiments are that they enable researchers to study independent variables that would be unethical or impractical to investigate in a laboratory or field experiment. However, a limitation of natural experiments is that researchers lack control over extraneous variables which reduces internal validity and makes it difficult to establish cause and effect relationship.
• Matched pairs design is when the researchers match the participants from the control and experimental groups for a particular participant variable.
• A strength of matched pairs is that researchers can establish a clearer cause and effect relationship between the independent variable and the dependent variable and researchers can control for some participant variables which increases the internal validity of the study. However, a limitation is that researchers can’t match participants on every possible participant variable and matching participants is time-consuming.
• Independent groups design is when researchers allocate different participants to each condition but don’t match the participants for any particular variables.
• Random allocation can be used to control participant variables in an independent groups design. This helps to control participant variables but doesn’t guarantee that all variables will be perfectly controlled.
• Repeated measures design is when the same participants take part in all of the experimental conditions.
• A limitation of repeated measures design is that participants are more likely to figure out the aim of the study by participating in all experimental conditions so are more likely to respond to demand characteristics. Also, the results can be influenced by order effects which is when the order of the experimental conditions influences the results of a study.
• Order effects can happen if the participant becomes better at a task due to practice, and also if the participants becomes less good at a task due to boredom.
• Counterbalancing is used to reduce order effects in repeated measures designs. It is when different participants are made to take part in the experimental conditions in different orders