Population: 18 40 Year olds – Prediction: Sleep deprived patients will have a higher BMI than non-sleep deprived subjects Extraneous variables (EV) (the word extraneous means ‘outside’ So an EV is any variable outside the experimental design that may affect the D.V, thereby having an unwanted effect on the results of the experiment and thus affecting the ability of the researchers to draw conclusions. So an EV is a variable other than the IV that may affect the DV They can occur at any stage of an experiment e.g. how the D.V was measured, how the – experimental group was treated (which may be different to treatment of control group) occur randomly rather than systematically i.e. they occur at a point of the EV’s – experiment Identification of extraneous potential confounding variables variable Description Example Alternatives Individual The composition of the control Control group has Use a repeated-measures participant and experimental groups, may 80% males, design to eliminate differences contain significant difference Experimental individual participant in terms of the intelligence, group has 80% differences or a past experience, memory females, gender pairs design to reduce ability, gender mix, age spread, may affect results individual participant etc which may influence the differences – results Non This involves subjects Comparing results Use standardised standardised receiving different instructions, of Psych class A instructions and instructions conducting experiment in a (experiment done procedures: i.e. same & procedures different context (different Monday am, to experimenter, same time of day, different location results of Psych context, etc. could affect results) class B – (experiment done Friday pm) Order effect (see below) Experimenter (see below) effect Placebo (see below) effect Placebo Effect & the use of a Placebo Placebo effect Explanation A tendency of participants expectations to influence their behaviour meaning that the IV is not the only variable influencing the value of the DV And/or the subjects knowing what group they are in (control or –
Population: 18 – 40 Year olds Prediction: Sleep deprived patients will have a higher BMI than non-sleep deprived subjects Extraneous variables (EV) (the word extraneous means ‘outside’ So an EV is any variable outside the experimental design that may affect the D.V, thereby having an unwanted effect on the results of the experiment and thus affecting the ability of the researchers to draw conclusions. So an EV is a variable other than the IV that may affect the DV They can occur at any stage of an experiment – e.g. how the D.V was measured, how the experimental group was treated (which may be different to treatment of control group) EV’s occur randomly rather than systematically – i.e. they occur at a point of the experiment Identification of extraneous potential confounding variables variable Description Example Alternatives Individual participant differences The composition of the control and experimental groups, may contain significant difference in terms of the intelligence, past experience, memory ability, gender mix, age spread, etc – which may influence the results Control group has 80% males, Experimental group has 80% females, gender may affect results Use a repeated-measures design to eliminate individual participant differences or a design to reduce individual participant differences Non standardised instructions & procedures This involves subjects receiving different instructions, conducting experiment in a different context (different time of day, different location – could affect results) Comparing results of Psych class A (experiment done Monday am, to results of Psych class B (experiment done Friday pm) Use standardised instructions and procedures: i.e. same experimenter, same context, etc. Order effect (see below) Experimenter effect (see below) Placebo effect (see below) Placebo Effect & the use of a Placebo Placebo effect Explanation A tendency of participants expectations to influence their behaviour meaning that the IV is not the only variable influencing the value of the DV And/or – the subjects knowing what group they are in (control or pairs
epsych_notes_-_cbc.docx