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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).
A hypothesis is a tentative statement about the relationship between two or
more variables. It is a specific, testable prediction about what you expect to happen in a
For example, a study designed to look at the relationship between sleep deprivation and
test performance might have a hypothesis that states, "This study is designed to assess the
hypothesis that sleep-deprived people will perform worse on a test than individuals who
are not sleep-deprived."
The Hypothesis in the Scientific Method
In the scientific method, whether it involves research in psychology,
biology, or some other area, a hypothesis represents what the
researchers think will happen in an experiment.1 The scientific method
involves the following steps:
1. Forming a question
2. Performing background research
3. Creating a hypothesis
4. Designing an experiment
5. Collecting data
6. Analyzing the results
7. Drawing conclusions
8. Communicating the results
Formulating a Hypothesis
In many cases, researchers might draw a hypothesis from a specific theory or
build on previous research. For example, prior research has shown that stress
can impact the immune system. So a researcher might hypothesize: "People
with high-stress levels will be more likely to contract a common cold after
being exposed to the virus than people who have low-stress levels."
In other instances, researchers might look at commonly held beliefs or folk
wisdom. "Birds of a feather flock together" is one example of folk wisdom
that a psychologist might try to investigate. The researcher might pose a
specific hypothesis that "People tend to select romantic partners who are
similar to them in interests and educational level."
Elements of a Good Hypothesis
So how do you write a good hypothesis? When trying to come up with a
hypothesis for your research or experiments, ask yourself the following
Is your hypothesis based on your research on a topic?
Can your hypothesis be tested?
Does your hypothesis include independent and dependent variables?
In the scientific method, falsifiability is an important part of any valid
hypothesis.1 In order to test a claim scientifically, it must be possible
that the claim could be proven false.
Students sometimes confuse the idea of falsifiability with the idea that
it means that something is false, which is not the case. What
falsifiability means is that if something was false, then it is possible
to demonstrate that it is false.
Types of hypothesis
Alternate Hypothesis
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
Examples of an alternative hypothesis:
"Children who receive a new reading intervention will
perform better than students who did not receive the
"Adults will perform better on a memory task than
Null Hypothesis
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.
Examples of a null hypothesis include:
"Children who receive a new reading intervention will have
scores different than students who do not receive the
"There will be no difference in scores on a memory recall task
between children and adults."
Nondirectional Hypothesis
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.
Directional Hypothesis
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.
Simple hypothesis: This type of hypothesis suggests that there is a
relationship between one independent variable and one dependent
Complex hypothesis: This type of hypothesis suggests a relationship
between three or more variables, such as two independent variables
and a dependent variable.
Statistical hypothesis: This hypothesis uses statistical analysis to
evaluate a representative sample of the population and then
generalizes the findings to the larger group.
Logical hypothesis: This hypothesis assumes a relationship between
variables without collecting data or evidence.