Laboratory Experiments

  • Control of independent variable
  • Control of extraneous variables

Lab experiments don’t have to be carried out in a laboratory.  However, any experiment that is carried out in a special, tightly controlled environment is classed as laboratory.  Importantly it is obvious to those taking part that that they are in an experimental procedure. Laboratory experiments are therefore artificial and tightly controlled, leading to the following advantages and disadvantages:

Cause and effect: We can usually see that the IV has caused the alteration in the DV.  Provided we have controlled our experiment we should be able to show that it was the coffee that was responsible for the faster reaction times.

Replication: Provided care has been taken in conducting and reporting the procedure another person should be able to repeat your procedure to see if they get the same results.

Lacks ecological validity: As with Milgram and studies into memory, laboratory experiments are very artificial.  Can they really tell us how people will behave in real life situations?

Demand characteristics: This refers to participants behaving differently because they know they are being watched.

Field Experiments

  • Control of independent variable
  • No control of extraneous variables

Experiment that are carried out in the natural environment, but with control of the independent variable. Likely settings would include the work place, school, the street etc.  Basically the same rules apply: an independent variable is manipulated to see how it affects a dependent variable.  Confounding variables can still get in the way, and cause and effect can still be determined.  However, the setting is more natural.

Ecological validity: Because the settings are more natural it is assumed that people will behave more naturally, so field experiments should have greater ecological validity.

Demand characteristics: These can be less since participants may not be aware that they are in an experiment, as was the case with Hofling!

Less control of variables: The experimenter has less control over the environment so more variables may affect the outcome.  As a result we cannot be certain that the IV has caused the change in DV.  Cause and effect relationships are therefore difficult to establish.

Ethics: If patients are unaware of the study how can the consent to take part or withdraw from the experiment?

Replication: It is difficult to repeat the procedure exactly as it was the first time.

Natural Experiments

  • No control of independent variable
  • No control of extraneous variables

Not, as the name implies, experiments carried out in the buff, although they could be if you were comparing the memory of those who naturally prefer to go au naturelle with those who prefer to wear clothes.  These are similar to and often confused with quasi-experiments, but there is one crucial difference.  Natural experiments take advantage of a naturally occurring event.  The effect of the eruption of Mount St Helens on stress related illnesses is the one all the texts prefer to mention.  In this case the IV was the eruption, a naturally occurring event.

A better example and one that we’ve studied is Hodges & Tizard’s study of institutional care which examined the effect of different types and duration of care on the children’s subsequent behaviour and development.

IV is the type and duration of care (in this case not controlled by the researchers, it happened anyway).  DV is the effect this has on subsequent development (and which can be measured using various tests).

Demand characteristics: It is often the case that the experimenter isn’t even present when the event occurs, thankfully in the case of Mt Saint Helens!  As a result participants are not trying to please the researchers.

Research opportunities: It is possible to research events that it would be unethical to study any other way or that may be impossible to set up.

Lack of control: The researchers have no control at all over the variables and there may be lots of confounding variables.  In the Mt St Helens case ill health caused by smoke, or stress due to loss of house etc.

Replication: In some cases clearly impossible, in others very difficult.  As a result it may be impossible to check the validity of research.

Cause and effect: Following on from lack of control, it may be impossible to decide if the IV is causing the change in the DV.