Control, demand characteristics and investigator effects

control measures

random allocation, counterbalancing, randomisation and standardisation

extraneous variables

any variable other than the IV that may affect the DV and therefore the results. Essentially nuisance variables that do not vary systematically with the IV (random)

confounding variables

EVs that vary systematically with the IV so cannot tell if the change in DV is due to IV or CV (not random)

Types of extraneous variables

situational variables and participant variables

situational variables

variables connected with the research situation

e.g. temp, time of day, lighting etc

controlled using standardisation

participant variables

variables connected with the research participants

e.g. age, intelligence, gender etc

controlled through the experimental design or random allocation

random allocation

randomly allocating participants to their groups

decreases participant variables

counterbalancing

combats order effects

split the sample in half, with 1 completing the 2 conditions in one order and the other completing it in the reverse order. Order effects should be balanced out

randomisation

trials are presented in random order to control the effects of bias

standardisation

all situational variables are kept identical - easy to replicate

the same formalised procedures and instructions for all participants

demand characteristics

can act as a confounding variable

cue from the researcher or research situation that may be interpreted by participants as revealing the purpose of the study, maybe leading participants to change their behaviour

Please-U effect = purposely tries to support the hypothesis

Screw-U effect = deliberately goes against the hypothesis

controlled by single-blind experiments - only researcher knows the true aims

participant reactivity

investigator effects

researcher acts in a way to support their prediction (conscious or unconscious)

controlled using a double-blind experiment in which both the researcher and participants are not aware

leading questions