Types of experiment

Question 1

Laboratory experiment

Answer 1

A controlled environment where extraneous and confounding variables can be regulated

Participants go to researcher

The IV is manipulated and the effect on the DV is recorded

Question 2

Lab - Eval

Answer 2

+ EVs and CVs can be controlled; this means that the effect of EVs and CVs on the DV can be minimised, cause and effect between the IV and DV can be demonstrated (high internal validity)

+ Can be more easily replicated; greater control means less chance that new EVs introduced, findings can be confirmed, supporting their validity

• May lack generalisability; the controlled lab environment may be rather artificial and participants are aware they are being studied, thus behaviour may not be ‘natural’ and can’t be generalised to everyday life (low external validity)
• Demand characteristics may be a problem; these are cues in the experimental situation that invite a particular response from participants, the findings may be explained by these cues rather than the effect of the IV (lower internal validity)

Question 3

Field experiment

Answer 3

A natural setting

The researcher goes to participants

The IV is manipulates and the effect on the DV is recorded

Question 4

Field - Eval

Answer 4

+ More natural environment; participants more comfortable and behaviour more authentic, results may be more generalisable to everyday life

+ Participants are unaware of being studied; they are more likely to behave as they normally do so the findings can be generalised, the study has greater external validity

• More difficult to control Evs/CVs; observed changes in the DV may not be due to the IV, but to the CVs/EVs instead, it is more difficult to establish cause and effect than in the lab
• There are ethical issues, participants in a field experiment may not have given informed consent, this is an invasion of the participants’ privacy, which raises ethical issues

Question 5

Natural experiment

Answer 5

The experiment does not manipulate the IV - it does change, but the change is not made by the experimenter - someone or something else causes the IV to vary. The IV would have varied even if the experimenter wasn’t interested

DV may be naturally occurring (e.g. exam results) or may be devised by the experimenter and measured in the field or a lab

Question 6

Natural - Eval

Answer 6

+ May be the only practical/ethical option; it may be unethical to mainpulate the IV, e.g. studying the effects of institutionalisation on children, a natural experiment may be the only way causal research can be done for such topics

+ Greater external validity; natural experiments involve real-world issues, such as the effect of a natural disaster on stress levels, the findings are more relevant to real experiences

• The natural event may only occur rarely; many natural events are ‘one-offs’ and this reduces the opportunity for research, this may limit the scope for generalising findings to other similar situation
• Participants are not randomly allocated; the experimenter has no control over which participants are placed in which condition as the IV is pre-exisitng, may result in CVs that aren’t controlled e.g. Romanian orphans adopted early may also be friendlier ones

Question 7

Quasi-experiment

Answer 7

IV is based on a pre-exisitng difference people, e.g. age or gender. No one has manipulated this variable, it simply exists

DV may be naturally occurring 9e.g. exam results) or may be devised by the experimenter and measured in the field or a lab

Question 8

Quasi - Eval

Answer 8

+ There is often high control; often carried out under controlled conditions and therefore shares some of the strengths of lab experiments, replication is possible

+ Comparisons can be made between people; the IV is a difference between people e.g. people with and without autism, comparisons between different types of people can be made

• Participants are not randomly allocated; the experimenter has no control over which participants are placed in which condition as the IV is pre-exisitng, participant variables may have caused the change in the DV acting as a CV
• Casual relationships not demonstrated; as with a natural experiment the researcher does not manipulate/control the IV, cannot say for certain that any change in the DV was due to the IV