— Overview
These notes answer an exam item on the research hypothesis (Ha) and the null hypothesis (Ho), on why a null is set in order to prove the research claim only indirectly, and on an example not given in the textbook. Setting a hypothesis, the writer says, is to choose a provisional theory that can be tested for the purpose of a study, and to examine it. Many modern papers use such a setting in order to secure the logic and the objectivity of the work.
The research hypothesis is what one aims to test, according to the purpose of the study; the null is the hypothesis that denies the claim under test. In a study, the null is what allows one to decide whether to reject or to accept the research hypothesis, and that is why a null is needed. The null should be understood not so much as the verbal opposite of the hypothesis under test as the claim that rejects it; the reason is to keep logical error as small as possible.
In other words, the opposite of “as A increases, B decreases” is not “as A increases, B increases,” but “A and B are unrelated.” An example offered here, and said not to appear in the textbook, concerns people who have studied abroad and their yearly income. The research hypothesis is that people who have been overseas to study will have a higher income than those who have not; the null is that whether one has studied abroad, and income, are unrelated.
The same exam packet continues into other items, on averages and on sampling, which are left aside here so the focus remains the hypotheses and the example. Among sources the notes list are Park Dae-su, Basic Probability and Statistics (Hanbit Academy, 2013); Park Jin-ho and Lee Geung-hui, The Concept of Probability and Its Applications (Korea National Open University Press, 2017); and Heo Myeong-hoe, A Guide to Statistical Surveys (Jayu Academy, 2011).
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— Contents and key concepts
What a research hypothesis is, and what a null is
These notes answer an exam item: to explain, briefly, the research hypothesis (Ha) and the null hypothesis (Ho); to explain, briefly, why a null is set in order to prove the research claim only indirectly; and to offer at least one example of a research hypothesis and a null that is not given in the textbook.
Setting a hypothesis, the writer says, is to choose a provisional theory that can be tested for the purpose of a study, and to examine it. Many modern studies and papers use such a setting, and the reason given here is that, by setting a hypothesis, one can secure the logic and the objectivity of the work.
Among hypotheses there are a research hypothesis and a null. The research hypothesis is what one aims to test, according to the purpose of the study; the null is the hypothesis that denies the claim under test. In a study, the null is what allows one to decide whether to reject or to accept the research hypothesis, and for that decision a null is needed.
Not a verbal opposite, but a claim that rejects
The null, the notes insist, should be understood not so much as the opposite of the hypothesis under test as the claim that rejects it. The reason is to keep logical error as small as possible.
In other words, the opposite of the sentence “as A increases, B decreases” is not “as A increases, B increases.” It should be set as “A and B are unrelated.” That, the writer says, is how a logical error can be avoided.
The distinction matters because a verbal contrary still asserts a relation, only in the other direction. A null that says the two are unrelated leaves the research claim to be tested against the absence of a relation, rather than against a rival story of the same form.
Overseas study and income, an example not in the book
An example of a research hypothesis and a null, the notes say, can help one understand the idea. The writer offers a case, said not to appear in the textbook, built on the relation between people who have studied abroad and their yearly income.
The research hypothesis is that people who have been overseas to study will have a higher income than those who have not. The null is that whether one has studied abroad, and income, are unrelated. The pair follows the rule already set out: the null does not claim that overseas study goes with a lower income, but that the two are without a relation.
The same exam packet continues into other items, on averages, medians and modes, and on sampling, which are left aside here so the focus remains the hypotheses and the example. Among sources the notes list are Park Dae-su, Basic Probability and Statistics (Hanbit Academy, 2013); Park Jin-ho and Lee Geung-hui, The Concept of Probability and Its Applications (Korea National Open University Press, 2017); and Heo Myeong-hoe, A Guide to Statistical Surveys (Jayu Academy, 2011). The same Korean report, at fuller length, is on CampusDown.
Sources
- A student exam answer on the research hypothesis and the null, and on why a null is set in order to prove a research claim only indirectly.
- The warning that the opposite of “as A increases, B decreases” is not “as A increases, B increases,” but “A and B are unrelated.”
- An example, said not to be in the textbook, about overseas study and income, with sources listed in the notes.
Last updated: 14 November 2026
Frequently asked questions
What, in these notes, is a research hypothesis, and what is a null?
Setting a hypothesis is to choose a provisional theory that can be tested for the purpose of a study, and to examine it. The research hypothesis (Ha) is what one aims to test, according to that purpose; the null (Ho) is the hypothesis that denies the claim under test. The null is what allows one to decide whether to reject or to accept the research hypothesis, and that is why it is needed.
Why is the null not set as the verbal opposite of the claim under test?
The null should be understood not so much as the opposite of the hypothesis under test as the claim that rejects it, in order to keep logical error as small as possible. The opposite of “as A increases, B decreases” is not “as A increases, B increases,” but “A and B are unrelated.”
What example, said not to be in the textbook, do the notes offer?
The example concerns people who have studied abroad and their yearly income. The research hypothesis is that people who have been overseas to study will have a higher income than those who have not; the null is that whether one has studied abroad, and income, are unrelated.
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