Types of experiment

Laboratory experiments

• Conducted in highly controlled environments

Laboratory strengths

• High control over confounding and extraneous variables. The researcher can ensure that any effect on the DV is likely the result of manipulation of the IV. We can be more certain about demonstrating cause and effect (high internal validity)

Laboratory strengths

• Replication is more possible than in other types of experiments because of the high level of control, ensuring that new extraneous variables are not introduced when repeating an experiment. Replication is vital to check the results of any study to see whether the finding is valid and not just a one-off

Laboratory weaknesses

• May lack generalisability. Environment is artificial and not like everyday life. In an unfamiliar context participants may behave in unusual ways so their behaviour cannot always be generalised beyond the research setting (low external validity)

Laboratory weaknesses

• Participants are usually aware they are being tested through this experiment (though they may not know why). This may give rise to 'unnatural' behaviour (demand characteristics)

Laboratory weaknesses

• Tasks participants are asked to carry out in this type of experiment may not represent everyday experience; for instance, recalling unconnected lists of words as part of a memory experiment (low mundane realism)

Field experiments

• Where the IV is manipulated in a natural, more everyday setting. The researcher goes to participants' usual environment rather than, in a lab experiment, participants going to a researcher's lab

Field strengths

• Higher mundane realism than lab experiments because the environment is more natural. Thus this type of experiment may produce behaviour that is more valid and authentic. This is especially the case as participants may be unaware they are being studied (high external validity)

Field weaknesses

• Price to pay for increased realism due to the loss of control of CVs and EV, meaning that cause and effect between the IV and DV in these studies may be much more difficult to establish and precise replication is often not possible

Field weaknesses

• There are ethical issues. If participants are unaware they are being studied they cannot consent to being studied and such research might constitute an invasion of privacy

Natural experiments

• Researcher measures the effect of an IV on a DV. However, the researcher has no control over the IV and cannot change it- someone or something causes the IV to vary. Participants can be tested anywhere, e.g. in a lab. DV may also be occurring in this sense (e.g. exam results) or may be devised by the experimenter and then measured in the field or lab

Natural strengths

• Provide opportunities for research that may not otherwise be undertaken for practical or ethical reasons, such as the studies of institutionalised Romanian orphans (Rutter et al)

Natural strengths

• Often have high external validity because they involve the study of real-world issues and problems as they happen, such as the effects of a natural disaster on stress levels

Natural weaknesses

• Events in this sense rarely happen, reducing the opportunities for research. This also may limit the scope for generalising findings to other similar situations

Natural weaknesses

• Participants may not be randomly allocated to experimental conditions (only happens when there is an independent groups design). This means the researcher might be less sure whether the IV affected the DV.

• E.g. in the study of Romanian orphans, the IV was whether children were adopted early or late. However, there was lots of differences between these groups, such as those adopted late may also have been less sociable than some of the other children, making them less appealing for prospective parents

Natural weaknesses

• Such research may be conducted in a lab and therefore may lack realism and demand characteristics may be an issue

Quasi-experiments

• Have an IV that is based on an existing difference between people (i.e. age or gender). No one has manipulated this variable, it simply exists and the IV cannot be changed. DV may be naturally occurring or may be devised by the experimenter and measured in the field or lab

• E.g. anxiety levels of phobic and non-phobic patients compared, the IV of 'having a 'phobia' would not have come about through manipulation

Quasi strengths

• Often carried out under controlled conditions and therefore share some strengths of a lab experiment (e.g. replication)

Quasi weaknesses

• Like natural experiments, this type of experiment cannot randomly allocate participants to conditions, and therefore there may be confounding variables

Quasi weaknesses

• In both this type of experiment and natural experiments, the IV is not intentionally changed by the researcher and therefore we cannot claim that the IV has caused any observed change