Variables, Aims and Hypotheses, directional and non-directional


The independent variable (IV) is the variable that psychologists manipulate/change to see if changing this variable has an effect on the dependent variable (DV).

The dependent variable (DV) is the variable that the psychologists measures (to see if the IV has had an effect).

It is important that the only variable that is changed in research is the independent variable (IV),  all other variables have to be kept constant across the control condition and the experimental conditions. Only then will researchers be able to observe the true effects of just the independent variable (IV) on the dependent variable (DV).


An aim is a clear and precise statement of the purpose of the study. It is a statement of why a research study is taking place. This should include what is being studied and what
the study is trying to achieve. (e.g. “This study aims to investigate the Aimeffects of alcohol on reaction times”.

It is important that aims created in research are realistic and ethical.


This is a testable statement that predicts what the researcher expects to happen in their research. The research study itself is therefore a means of testing whether or not the hypothesis is supported by the findings. If the findings do support the hypothesis then the hypothesis can be retained (i.e., accepted), but if not, then it must be rejected.

Three Different Hypotheses:

(1) Directional Hypothesis: states that the IV will have an effect on the DV and what that effect will be (the direction of results). For example, eating smarties will sBitcoin-Price-Prediction-300x201ignificantly improve an individual’s dancing ability. When writing a directional hypothesis, it is important that you state exactly how the IV will influence the DV.

(2) Non-Directional Hypothesis: hypothesis simply states that the IV will have an effect on the DV but does not predict how it will affect the results. For examp
le, ‘eating smarties will have a significant affect on an individual’s dancing ability.’

(3) A Null Hypothesis: states that the IV will have no significant effect on the DV, for example, ‘eating smarties will have no effect in an individuals dancing ability.’

Exam Tip: One of the questions that you may get asked in the exam is ‘when would a psychologist decide to use a directional hypothesis?’ In general, psychologists use a directional hypothesis when there has been previous research on the topic that they aim to investigate (the psychologist has a good idea of what the outcome of the research is going to be). For example, if a researcher was going to carry research out of the effects of alcohol on reaction times, they would predict a directional hypothesis due to the fact that there has already been lots of research looking at this area.