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Research methods
Internal validity
How much does the experiment investigate what it actually wants to find
out? I.e. how accurate is it?
Extraneous variables affect the internal validity of an investigation:
There are many different types of extraneous variables which clearly impact the
internal validity of the investigation:
Situational: temperature, instructions or time of day
Participant: intelligence, age, gender
Demand characteristics: reduced by a single blind design (don't tell the
participant about the aim of the experiment)
Investigator effects: reduced by a double blind design (don't tell the
participant or the investigator about the aim of the study. Get another
person to conduct the experiment instead of the investigator, who doesn't
know the aim either.
External validity
Accuracy of generalising findings to other situations
Ecological validity: the artificially of a lab experiment can alter the
behaviour of the individuals so that in real life they would behave
differently. If this occurs then the study lacks mundane realism or
ecological validity
Population validity: clearly the sample can affect the population validity as
if it is biased it won't represent the target population and the results won't
be able to be generalised to the whole target population.


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