By Saul McLeod, updated Dec 16, 2021
A hypothesis (plural hypotheses) is a precise, testable statement of what the researcher(s) predict will be the outcome of the study. It is stated at the start of the study.
This usually involves proposing a possible relationship between two variables: the independent variable (what the researcher changes) and the dependent variable (what the research measures).
In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).
A fundamental requirement of a hypothesis is that is can be tested against reality, and can then be supported or rejected.
To test a hypothesis the researcher first assumes that there is no difference between populations from which they are taken. This is known as the null hypothesis. The research hypothesis is often called the alternative hypothesis.
Types of research hypotheses
The alternative hypothesis states that there is a relationship between the two variables being studied (one variable has an effect on the other).
An experimental hypothesis predicts what change(s) will take place in the dependent variable when the independent variable is manipulated.
It states that the results are not due to chance and that they are significant in terms of supporting the theory being investigated.
The null hypothesis states that there is no relationship between the two variables being studied (one variable does not affect the other). There will be no changes in the dependent variable due to the manipulation of the independent variable.
It states results are due to chance and are not significant in terms of supporting the idea being investigated.
A non-directional (two-tailed) hypothesis predicts that the independent variable will have an effect on the dependent variable, but the direction of the effect is not specified. It just states that there will be a difference.
E.g., there will be a difference in how many numbers are correctly recalled by children and adults.
A directional (one-tailed) hypothesis predicts the nature of the effect of the independent variable on the dependent variable. It predicts in which direction the change will take place. (i.e. greater, smaller, less, more)
E.g., adults will correctly recall more words than children.
The Falsification Principle, proposed by Karl Popper, is a way of demarcating science from non-science. It suggests that for a theory to be considered scientific it must be able to be tested and conceivably proven false.
For Popper, science should attempt to disprove a theory, rather than attempt to continually support theoretical hypotheses.
Can a hypothesis be proven?
How to write a hypothesis
What are examples of a hypothesis?
Let’s consider a hypothesis that many teachers might subscribe to: that students work better on Monday morning than they do on a Friday afternoon (IV=Day, DV=Standard of work).
Now, if we decide to study this by giving the same group of students a lesson on a Monday morning and on a Friday afternoon and then measuring their immediate recall on the material covered in each session we would end up with the following:
The null hypothesis is, therefore, the opposite of the alternative hypothesis in that it states that there will be no change in behavior.
At this point, you might be asking why we seem so interested in the null hypothesis. Surely the alternative (or experimental) hypothesis is more important?
Well, yes it is. However, we can never 100% prove the alternative hypothesis. What we do instead is see if we can disprove, or reject, the null hypothesis.
If we reject the null hypothesis, this doesn’t really mean that our alternative hypothesis is correct – but it does provide support for the alternative / experimental hypothesis.
How to reference this article:
McLeod, S. A. (2018, August 10). What is a hypothesis. Simply Psychology. www.simplypsychology.org/what-is-a-hypotheses.html
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