First 199 words of the document:
Research methods revision
How much does the experiment investigate what it is actually supposed to be
measuring? How accurate is it?
Extraneous variables: affect the internal validity of the investigation
Situational: temperature, instructions or the time of day
Participant: intelligence, gender
Demand characteristics: reduced by a single blind design (don't tell the
participant the aim of the experiment)
Investigator effects: reduced by a double blind design (don't tell the
participant of the investigator the aim of the experiment) get another
person to conduct the experiment instead of the investigator who doesn't
know the aim either.
External validity: accuracy of generalising to other situations
Ecological validity: lab experiments are artificial so they can alter the
behaviour of the participants so that in real life they would behave
differently causing the study to lack mundane realism or ecological validity.
Population validity: if the sample is biased it won't represent the target
population and so the results won't be generalised to the whole population
and so the experiment would lack population validity.