Variables and hypotheses in psychology research

Variables
Independent variables
These are the variable(s) that the experimenter manipulates or changes, for example if a researcher were interested in comparing short-term memory capacity in males and females then the independent variable would be gender (he cannot change participants' genders, but he can assign people of different genders to the experimental groups he uses).

Dependent variables
These are the variables that the experimenter measures - their value depends on how the independent variable has been set. In the above example the dependent variable is short-term memory capacity. Dependent variables need to be operationalised before they can be measured.

Operationalising variables
A variable is operationalised when it has been turned in to something that can be measured. ‘Memory’ is a variable, but how can it be measured? ‘Memory as measured by the number of items correctly recalled from a list after 5 minutes’ is an operationalised variable. Similarly ‘aggression’ could be operationalised as the number of aggressive acts recorded in a 10 minute observation.

Extraneous variables
These are any variables other than the independent variable that may affect the dependent variable in some way. In the above example time of day could be an extraneous variable as people may be more vigilant at one time of day and less so at another. Other examples could be intelligence level of participants, age of participants, temperature, etc. Extraneous variables therefore need to be controlled in order to reduce or eliminate the influence they have on the DV, which basically means they need to be the same for al participants. In this example it would be sufficient to test all participants at the same time of day and thus eliminate any difference in time of day.



Hypotheses
Directional hypotheses
A directional prediction of what is expected to happen. It states which condition of the IV will perform better or worse than the other. It must include the DV and be operationalised.
  • Male participants will score more basketball hoops than female participants.
  • Participants whop have been trained in a memory improvement strategy will correctly recall more items from a list than participants who have not been trained.

Nondirectional hypotheses
A nondirectional prediction of what is expected to happen. It states that there will be a difference between the conditions of the IV, but it does not state which will perform better or worse. It must include the DV and be operationalised.
  • There will be a difference between male and female participants in the number of basketball hoops scored.
  • There will be a difference in the number of items correctly recalled from a list between participants who have had memory improvement training and those who have not.

Null hypotheses
A statement that nothing will happen. It states there will be no difference between the conditions of the IV. It must include the DV and be operationalised. It is an important statement as the purpose of empirical research is to reject or disprove the null hypothesis, and so lend support to the prediction made in one of the experimental hypotheses.
  • There will be no difference between male and female participants in the number of basketball hoops scored.
  • There will be no difference between participants who have been trained in memory improvement strategies and those who have not in the number of items correctly recalled from a list.


A Level exam tips
Answering exam questions (PSYA1 AQA A specification)
These tend to be 1 or 2 mark questions focused on showing you understand how to identify and operationalise variables, and how to write an hypothesis.
  • What was the IV in this study? For a 1 mark answer you would simply state the IV (e.g. short term memory performance), and for 2 marks you would also need to say how it was operationalised (e.g. number of items correctly recalled from a list).
  • Write an appropriate directional hypothesis for this study. For 1 mark you would need to write a basic directional hypothesis including the IV and DV. The second mark would be awarded if you have operationalised the IV and DV correctly (i.e. stated how they were measured).









Keywords: operationalising variables, operationalizing variables, dependent variable, independent variable, extraneous variable, directional hypothesis, nondirectional hypothesis, null hypothesis