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Hypothesis

A hypothesis is a provisional idea whose merit requires further evaluation. In research, a hypothesis must be stated in operational terms to allow its soundness to be tested.

The term hypothesis derives from the Greek (

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), which means “to put under” or “to suppose.” A scientific hypothesis is not the same as a scientific theory, even though the words hypothesis and theory are often used synonymously in common and informal usage. A theory might start as a hypothesis, but as it is subjected to scrutiny, it develops from a single testable idea to a complex framework that although perhaps imperfect has withstood the scrutiny of many research studies.

This entry discusses the role of hypotheses in research design, the types of hypotheses, and writing hypothesis.

Hypothesis in Research Design

Two major elements in the design of research are the researcher's hypotheses and the variables to test them. The hypotheses are usually extensions of existing theory and past research, and they motivate the design of the study. The variables represent the embodiment of the hypotheses in terms of what the researcher can manipulate and observe.

A hypothesis is sometimes described as an educated guess. However, this statement is also questioned to be a good description of hypothesis. For example, many people might agree with the hypothesis that an ice cube will melt in less than 30 minutes if put on a plate and placed on a table. However, after doing quite a bit of research, one might learn about how temperature and air pressure can change the state of water and restate the hypothesis as an ice cube will melt in less than 30 minutes in a room at sea level with a temperature of 20C or 68F. If one does further research and gains more information, the hypothesis might become an ice cube made with tap water will melt in less than 30 minutes in a room at sea level with a temperature of 20 C or 68F. This example shows that a hypothesis is not really just an educated guess. It is a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. In other words, a hypothesis is a tentative statement about the expected relationship between two or more variables. The hypothesis is tentative because its accuracy will be tested empirically.

Types of Hypotheses

Null Hypothesis

In statistics, there are two types of hypotheses: null hypothesis (H0) and alternative/research/maintained hypothesis (Ha). A null hypothesis (H0) is a falsifiable proposition, which is assumed to be true until it is shown to be false. In other words, the null hypothesis is presumed true until statistical evidence, in the form of a hypothesis test, indicates it is highly unlikely. When the researcher has a certain degree of confidence, usually 95% to 99%, that the data do not support the null hypothesis, the null hypothesis will be rejected. Otherwise, the researcher will fail to reject the null hypothesis.

In scientific and medical applications, the null hypothesis plays a major role in testing the significance of differences in treatment and control groups. Setting up the null hypothesis is an essential step in testing statistical significance. After formulating a null hypothesis, one can establish the probability of observing the obtained data.

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