Types of Experiments.

In Psychology, there are many ways to obtain data. The big three are:

Field 

They are conducted in the everyday, or natural environment of the participants, but situations are artificially set up.

The experimenter manipulates the IV, but in a real life setting, so hence he has no control over extraneous variables.

Strengths:

• High in ecological validity
• Participants are unaware of the experiment - avoid demand characteristics

Limitations:

• Experiments are much harder to control confounding variables
• Time consuming experiments, and expensive 

In field experiments it is not usually possible to gain informed consent from the participants and it is difficult to debrief the participants.

Laboratory Experiments

The features of this kind of experiment is that it takes place in an environment designed to maximize control over extraneous variables to help ensure the validity of the study. The environment is  well-controlled, and accurate measurements are possible.

The researcher decides where the experiment will take place, at what time, with which participants, in what circumstances and using what procedures. You can more easily eliminate confounding variables, and get clear results.

Strengths:

• It is usually the method with the highest level of reliability
• It allows valid cause-effect conclusions in terms of the variables measured because of the certainty gained by control over extraneous variables.

This precision then allows for easy replication of the experiment, which makes it more likely to be checked and confirmed by other researchers.

Limitations:

• Too high level of control over variables, which means that the whole situation become artificial or unrealistic.
• Ecological validity is low, and results cannot be generalized beyond the experimental situation.

 

Natural (quasi)

A quasi experiment is where the independent variable is not manipulated by the researcher but occurs naturally.

 

In a true experiment participants are allocated to the conditions of an experiment, usually through random assignment, however this is not always possible for practical or ethical reasons.

In a quasi experiment the researcher takes advantage of pre-existing conditions such as age, sex or an event that the researcher has no control over such as a participants’ occupation.

 

Strengths:

• A strength of quasi experiments is that that they are taking part in an investigation
•  May not be as artificial as laboratory experiments.

Limitations:

•  harder to establish causal relationships (because the independent variable is not being directly manipulated by the researcher.)

It is worth noting that quasi experiments are very common in psychology because ethically and practically they are the only design that can be used.