Null Hypothesis & Alternative Hypothesis - Research Aptitude Notes

Hypothesis

• A hypothesis is an assumption or concession made for the sake of argument
• It is an interpretation of a practical situation or condition taken as the ground for action
• It is a tentative assumption made in order to draw out and test its logical or empirical consequences.
• It is a proposition in testable form and predicts a particular relationship between two or more variables. If a researcher thinks that a relationship exists, he should first state it as a hypothesis and then test the hypothesis in the field.
• In research, the hypothesis is written in two types, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).

Null Hypothesis

• The null hypothesis states that there is no difference between the two phenomena or situation being studied.
• In this, one variable does not have any effect on another variable.
• It is denoted by H0.

Example: 

• If the hypothesis is given that “the consumption of a particular ayurvedic medicine reduces the chances of cancer”, the null hypothesis will be “the consumption of the ayurvedic medicine doesn’t reduce the chances of cancer.” It means there is no relationship between Ayurvedic medicine and cancer in the above given hypothesis.
• If the hypothesis is given that, “If random test results are collected from boys and girls, does the score of one group differ from the other?” a possible null hypothesis will be that the mean test results of boys is the same as that of the girls. It means the hypothes given above proves that there is no relationship based on goup and test score.

Alternative Hypothesis

• The alternative hypothesis states that there is a relationship between the two variables.
• It means one variable has an impact or effect on another variable.
• It is denoted by H1.
• This hypothesis can be simply termed as an alternative to the null hypothesis.
• In this, the hypothesis that is to be proved that indicates that the results of a study are significant and that the sample observation is not results just from chance but from some non-random cause.

Example:

• If the hypothesis is given that “the consumption of a particular ayurvedic medicine reduces the chances of cancer”, the alternate hypothesis will be “the consumption of that particular ayurvedic medicine reduce the chances of cancer.” It means there is a relationship between Ayurvedic medicine and cancer in the above given hypothesis.
• If the hypothesis is given that, “If random test results are collected from boys and girls, does the score of one group differ from the other?” an alternate hypothesis will be that the mean test results of boys that of the girls are different. It means the hypothesis given above prove that there is a relationship based on group and test score.

Directional Hypothesis

• It predicts the nature of the effect of the independent variable on the dependent variable.
• The researcher makes a prediction by on positive or negative impact, or relationship between two variables. 
• This prediction made by researcher is typically based on past research, accepted theory, extensive experience, or literature on the topic.
• E.g., Adults will correctly recall more words than children.

Nondirectional Hypothesis

• It predicts the nature of the effect of the independent variable on the dependent variable. But the direction is not specified. Whether the impact will be positive or negative is not specified.
• E.g., there will be a difference in how many numbers are correctly recalled by children and adults.

How to Write a Hypothesis

1. To write the alternative and null hypotheses for an investigation, the researcher needs to identify the main variables in the research.
2. Researcher manipulates the independent variable and the outcome is a dependent variable which is measured.
3. Defining the variables in research. It means how the researcher will define and measure the particular variable used in research.
4. Deciding the direction of prediction in the hypothesis. If there is evidence to support the effect of the independent variable on dependent variable..
5. Writing the hypothesis. A good hypothesis is short, clear, concise and in simple language.

What Are Examples of a Hypothesis?

• Let’s consider a hypothesis that many managers in office might subscribe to that employees work better on Monday morning than they do on a Friday afternoon (Independent Variable=Day, Dependent Variable=Standard of work).
• Now, if we decide to study this by giving the same group of employees work on a Monday morning and on a Friday afternoon and then measuring their work we would end up with the following:
• The alternative hypothesis states that employees did more work on a Monday morning than on a Friday afternoon.
• The null hypothesis states that there will be no significant difference in the amount of work done on a Monday morning compared to a Friday afternoon. The null hypothesis is, therefore, the opposite of the alternative hypothesis in that it states that there will be no change in the work doner.
• 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.