Control variables

Extraneous variables

Any other variable which is not the IV that affects the DV and does not vary systematically with the IV. Eg. lighting in the lab or the age of Ps — These variables of not confound the results of a study but just make them harder to detect.

Confounding variables

Also a variable that has an effect on the DV that is not the IV.

They do change systematically with the impact of the IV. It becomes difficult for the researcher to be sure of the origin of the impact of the DV as confounding variables could have been the cause.

Demand characteristics

Any cue the researcher or research situation may give which makes the participant feel like they can guess the Ian of the investigation. This can cause the participant to act differently in the research situation to how they would normally act.

Participant reactivity

Participants may change their behaviour to fit the situation rather than acting naturally.

‘Please-U’ and ‘Screw-U’ effect

• Please-U — Acting in the way they think the researcher wants them to act.

• Screw-U — Intentionally underperform to sabotage the study’s results.

Affects validity

Investigator effects

Any unwanted influence from the researcher’s behaviour, either conscious or unconscious, on the DV.

Randomisation

The use of chance to reduce the effects of bias from investigator effects. Eg. selection of Ps

Standardisation

Using the exact same formalised procedures and instructions for every single participant involved in the research process.