Types of Experiment (AQA A-Level Psychology): Revision Notes

Types of Experiment

Laboratory experiments

Laboratory experiments are conducted in controlled environments, allowing researchers to establish causality through precise manipulation of variables. These studies, such as Baddeley's (1966) encoding in memory research, take place in controlled settings using standardised procedures with randomly allocated experimental groups.

Advantages of laboratory experiments

• Laboratory experiments offer exceptional high degree of control. Experimenters control all variables, with the independent variable (IV) and dependent variable (DV) precisely operationalised and measured. This leads to greater accuracy and objectivity in results.
• Replication becomes possible when other researchers can repeat the experiment exactly to verify results. This scientific rigour strengthens the reliability of findings.
• The controlled environment enables researchers to establish cause and effectrelationships. Since all other variables are controlled, any change in the DV must result from the manipulation of the IV.
• Additionally, laboratory settings allow for isolation of variables. Individual pieces of behaviour can be isolated and rigorously tested without interference from external factors.

Weaknesses of laboratory experiments

• Despite their scientific rigour, laboratory experiments face several limitations. Experimenter bias can affect results when experimenters' expectations influence both their behaviour and participants' responses.
• Problems with operationalisation arise when researchers define variables too specifically. For example, defining 'getting fatter' as gaining two pounds per week may not relate meaningfully to real-world weight gain patterns.
• Low external (ecological) validity represents a major concern. The highly controlled, artificial laboratory environment differs substantially from real life, making it difficult to generalise results to other settings. Laboratory environments can feel intimidating, causing people to behave unnaturally.
• Demand characteristics occur when participants become aware they're being tested and unconsciously alter their behaviour accordingly.

Field experiments

Field experiments occur in 'real world' settings rather than laboratories, with participants often unaware they're in a study. The IV remains manipulated by the experimenter, but as many other variables as possible are controlled. Bickman's (1974) obedience study exemplifies this approach.

Natural and quasi experiments

Natural experiments involve situations where the IV varies naturally rather than through experimenter manipulation. The researcher records the effect on the DV without directly manipulating variables.

Quasi experiments occur when researchers cannot freely manipulate the independent variable or randomly allocate participants to different conditions. These studies often examine naturally occurring variables such as gender differences, where males and females are compared on various measures.

Both natural and quasi experiments are frequently employed when manipulating an IV would be unethical, such as studying the effects of poverty or trauma on development.

Advantages of field and natural experiments

• High ecological validity represents the primary strength of these approaches. Results relate directly to everyday behaviour and can be generalised to other real-world settings because they occur in natural environments.
• No demand characteristics typically exist since participants are often unaware they're in an experiment, eliminating artificial behaviour changes that might occur in laboratory settings.

Weaknesses of field and natural experiments

• Less control over extraneous variables makes it more difficult to establish clear causality. Other factors may influence the results, making it harder to determine what specifically caused observed changes.
• Replication becomes challenging since natural conditions are never exactly identical. Field and natural experiments cannot be repeated under precisely the same circumstances to verify results.
• Ethics concerns arise when participants are unaware they're in an experiment, raising issues about informed consent. This applies particularly to field experiments, since natural/quasi experiments involve naturally occurring variables not manipulated by experimenters.
• Sample bias may occur since participants aren't randomly allocated to groups, meaning samples may not be comparable to each other, potentially affecting the validity of comparisons.