extraneous variables

• The presence of these could cause an error, potentially showing a causal relationship between the IV and DV that is not really there, or hiding one,
• Demand characteristics- if the participant thinks that they have discovered the aim, they may alter their behaviour to match what the researcher wants, this could be due to cues from the researcher (eg tone of voice/body language) or the set up that makes the aim obvious
• participant variables- in independent groups design if there are more people with relevant characteristics, prior knowledge or skills related to the task in one condition this can result in a difference in performance between conditions unrelated to the IV.
• situational variables- environmental factors present in one condition but not the other condition that could reasonably lead to a change in behaviour between the conditions. This could be related to temperature, noise or visual differences
• confounding variables- a variable other than the IV that changes systematically between the levels of IV. Meaning as you change the IV you also change the confounding variable, this then hides the IV's true effect (or lack of effect) on the DV as the researcher is measuring the confounding variables' influence in addition to the IV's
• controlling extraneous variables- actions taken to minimise the effect of extraneous variables on the DV. Random allocation- removes potential bias in assigning more pps with relevant characteristics to one condition in an independent groups design, however more pps with relevant characteristics can end up in one group due to chance
• participant variables- matched pairs design- relevant characteristics are measured before the study and the top two participants are randomly assigned to separate groups
• order effects- counterbalancing- attempts to control for (does not eliminate) order effects, this uses the ABBA format, half pps complete condition A first and B second, and the other half of the sample start with condition B then A, this means the order effects such as practice influences each condition equally
• situational variables- standardised procedures- any aspects of the environment that could (reasonably)influence the results that are listed in standardised procedures. This list could also include a script of standardised instructions that is read in the same way to each participant. By standardising the experiment researcher ensures that each participant has the same experience aside from the variation in the IV.
• Demand characteristics- single and double blind trials - single blind- pp is not aware of the aim of the aim of the experiment, double blind- both the pp and researcher who is directly testing the participant do not know the aim of the experiment, This is to stop the researcher (consciously/unconsciously) from influencing the pps behaviour with their body language/tone of voice. Standardising procedures/scripts also reduce the likelihood of demand characteristics
• pilot studies aims- to improve the quality of the main research study by assessing the experience of participants in the pilot. eg pilot studies can reveal- unexpected extraneous variables that need controlling, the pps may feel they have discovered the aim and acted according to demand characteristics,
• peer review- before publication the researcher needs to show off their written up study to other experts in their field, as part of the peer review process unaccounted for variables may be identified that have confounded the results, however this may mean the study lacks internal validity and will need repeating