7.2.8 Variables

Dependent Variable

• This is the factor which is measured in the study to assess the effect of the IV, for example:
  • the number of items recalled from a list of 20
  • the time taken in seconds to complete a jigsaw puzzle
  • the number of imitative acts of aggression performed in a 20-minute observation schedule
• The DV depends on how the IV has been set up: if the IV is whether participants learn/memorise something with loud music playing or in silence then it makes sense that the DV is ‘the number of….’ or ‘the time taken to…’ i.e. it must be quantitative 
• It is impossible to have a qualitative DV: the measure will always take some form of numerical data which can then be displayed in a graph or percentages etc.

Independent Variable 

• In psychological research, psychologists are interested in human behaviour and how it is affected and impacted by various factors
• To study the effects of specific variables on behaviour it is necessary to change/manipulate and measure different factors 
• The independent variable (IV) is the factor which is changed/manipulated to observe the effect it has on the dependent variable (DV) for example:
  • whether participants learn a list of 20 words in silence or in the presence of loud rock music (the IV = silence or loud rock music)
  • whether participants complete a jigsaw puzzle after 30 minutes exercise or after no exercise (the IV = 30 minutes exercise or no exercise)
  • whether participants have been exposed to an aggressive adult model or not (the IV = aggressive adult model or no aggressive adult model)
• A laboratory experiment must use an IV that has been implemented by the researcher e.g. loud music or silence; the IV cannot be naturally-occurring e.g. gender, age, ethnicity

Extraneous & Confounding Variables 

• Extraneous variables are any factors that intrude upon and adversely affect the DV (i.e.not the IV, which the researcher has specifically implemented) for example:
  • time of day (some participants may be 'morning people' which means that they are likely to be more alert first thing compared to others)
  • temperature (if the experimental space is too warm/cold it may affect participant performance on the task)
  • mood (one participant may have just had a row with their partner or won some money or feel a bit ‘off’ that day: any of these events mean that their mood is likely to affect their performance on the task)
• Extraneous variables are usually controlled so they have the same effect across all conditions, which should stop them affecting the DV, for example:
  • time of day: run the experiment at midday which should hopefully be a neutral time for everyone
  • temperature: ensure the experimental space has an ambient temperature 
  • mood: treat participants in a friendly but neutral way, to avoid adding to any existing mood
• If extraneous variables are not controlled then they can become confounding variables 
• Confounding variables can affect the DV and impact the outcome of the research
• The interference of confounding variables may not be apparent until after the research process has been completed, in which case a researcher should acknowledge the possibility of such interference in the discussion section of the psychological report (more on this in the revision note: Sections of a Report)

Operationalising Variables 

• This is the process of transforming variables into measurable factors
• All variables have to be operationalised, meaning they have to be clearly defined and set in motion
• Being clearly defined allows for manipulation of the independent variable and also means the dependent variable can be precisely measured for example:
  • reconstructive memory was operationalised by Loftus & Palmer (1974) as exposure to one of five verbs (the IV) which varied in strength (e.g. 'smashed', 'contacted'); the DV was operationalised as the speed estimate per participant in miles per hour
• Sometimes, it is difficult to measure all variables, especially with human behaviour (e.g., motivation of the participant)
• However, if not all variables are measured proprerly, it can make the results unreliable as the research will not be able to be replicated, meaning it also effects the validity of the research