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What Are the Elements of a Good Hypothesis?

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Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
B.A., Physics and Mathematics, Hastings College

A hypothesis is an educated guess or prediction of what will happen. In science, a hypothesis proposes a relationship between factors called variables. A good hypothesis relates an independent variable and a dependent variable. The effect on the dependent variable depends on or is determined by what happens when you change the independent variable . While you could consider any prediction of an outcome to be a type of hypothesis, a good hypothesis is one you can test using the scientific method. In other words, you want to propose a hypothesis to use as the basis for an experiment.

Cause and Effect or 'If, Then' Relationships

A good experimental hypothesis can be written as an if, then statement to establish cause and effect on the variables. If you make a change to the independent variable, then the dependent variable will respond. Here's an example of a hypothesis:

If you increase the duration of light, (then) corn plants will grow more each day.

The hypothesis establishes two variables, length of light exposure, and the rate of plant growth. An experiment could be designed to test whether the rate of growth depends on the duration of light. The duration of light is the independent variable, which you can control in an experiment . The rate of plant growth is the dependent variable, which you can measure and record as data in an experiment.

Key Points of Hypothesis

When you have an idea for a hypothesis, it may help to write it out in several different ways. Review your choices and select a hypothesis that accurately describes what you are testing.

Does the hypothesis relate an independent and dependent variable? Can you identify the variables?
Can you test the hypothesis? In other words, could you design an experiment that would allow you to establish or disprove a relationship between the variables?
Would your experiment be safe and ethical?
Is there a simpler or more precise way to state the hypothesis? If so, rewrite it.

What If the Hypothesis Is Incorrect?

It's not wrong or bad if the hypothesis is not supported or is incorrect. Actually, this outcome may tell you more about a relationship between the variables than if the hypothesis is supported. You may intentionally write your hypothesis as a null hypothesis or no-difference hypothesis to establish a relationship between the variables.

For example, the hypothesis:

The rate of corn plant growth does not depend on the duration of light.

This can be tested by exposing corn plants to different length "days" and measuring the rate of plant growth. A statistical test can be applied to measure how well the data support the hypothesis. If the hypothesis is not supported, then you have evidence of a relationship between the variables. It's easier to establish cause and effect by testing whether "no effect" is found. Alternatively, if the null hypothesis is supported, then you have shown the variables are not related. Either way, your experiment is a success.

Need more examples of how to write a hypothesis ? Here you go:

If you turn out all the lights, you will fall asleep faster. (Think: How would you test it?)
If you drop different objects, they will fall at the same rate.
If you eat only fast food, then you will gain weight.
If you use cruise control, then your car will get better gas mileage.
If you apply a top coat, then your manicure will last longer.
If you turn the lights on and off rapidly, then the bulb will burn out faster.
What Is a Testable Hypothesis?
What Is a Hypothesis? (Science)
What Are Examples of a Hypothesis?
Scientific Hypothesis Examples
Six Steps of the Scientific Method
Scientific Method Flow Chart
Null Hypothesis Examples
Understanding Simple vs Controlled Experiments
Scientific Method Vocabulary Terms
Scientific Variable
What Is an Experimental Constant?
What Is a Controlled Experiment?
What Is the Difference Between a Control Variable and Control Group?
DRY MIX Experiment Variables Acronym
Random Error vs. Systematic Error
The Role of a Controlled Variable in an Experiment

Educational resources and simple solutions for your research journey

Research hypothesis: What it is, how to write it, types, and examples

What is a Research Hypothesis: How to Write it, Types, and Examples

Any research begins with a research question and a research hypothesis . A research question alone may not suffice to design the experiment(s) needed to answer it. A hypothesis is central to the scientific method. But what is a hypothesis ? A hypothesis is a testable statement that proposes a possible explanation to a phenomenon, and it may include a prediction. Next, you may ask what is a research hypothesis ? Simply put, a research hypothesis is a prediction or educated guess about the relationship between the variables that you want to investigate.

It is important to be thorough when developing your research hypothesis. Shortcomings in the framing of a hypothesis can affect the study design and the results. A better understanding of the research hypothesis definition and characteristics of a good hypothesis will make it easier for you to develop your own hypothesis for your research. Let’s dive in to know more about the types of research hypothesis , how to write a research hypothesis , and some research hypothesis examples .

Table of Contents

What is a hypothesis ?

A hypothesis is based on the existing body of knowledge in a study area. Framed before the data are collected, a hypothesis states the tentative relationship between independent and dependent variables, along with a prediction of the outcome.

What is a research hypothesis ?

Young researchers starting out their journey are usually brimming with questions like “ What is a hypothesis ?” “ What is a research hypothesis ?” “How can I write a good research hypothesis ?”

A research hypothesis is a statement that proposes a possible explanation for an observable phenomenon or pattern. It guides the direction of a study and predicts the outcome of the investigation. A research hypothesis is testable, i.e., it can be supported or disproven through experimentation or observation.

Characteristics of a good hypothesis

Here are the characteristics of a good hypothesis :

Clearly formulated and free of language errors and ambiguity
Concise and not unnecessarily verbose
Has clearly defined variables
Testable and stated in a way that allows for it to be disproven
Can be tested using a research design that is feasible, ethical, and practical
Specific and relevant to the research problem
Rooted in a thorough literature search
Can generate new knowledge or understanding.

How to create an effective research hypothesis

A study begins with the formulation of a research question. A researcher then performs background research. This background information forms the basis for building a good research hypothesis . The researcher then performs experiments, collects, and analyzes the data, interprets the findings, and ultimately, determines if the findings support or negate the original hypothesis.

Let’s look at each step for creating an effective, testable, and good research hypothesis :

Identify a research problem or question: Start by identifying a specific research problem.
Review the literature: Conduct an in-depth review of the existing literature related to the research problem to grasp the current knowledge and gaps in the field.
Formulate a clear and testable hypothesis : Based on the research question, use existing knowledge to form a clear and testable hypothesis . The hypothesis should state a predicted relationship between two or more variables that can be measured and manipulated. Improve the original draft till it is clear and meaningful.
State the null hypothesis: The null hypothesis is a statement that there is no relationship between the variables you are studying.
Define the population and sample: Clearly define the population you are studying and the sample you will be using for your research.
Select appropriate methods for testing the hypothesis: Select appropriate research methods, such as experiments, surveys, or observational studies, which will allow you to test your research hypothesis .

Remember that creating a research hypothesis is an iterative process, i.e., you might have to revise it based on the data you collect. You may need to test and reject several hypotheses before answering the research problem.

How to write a research hypothesis

When you start writing a research hypothesis , you use an “if–then” statement format, which states the predicted relationship between two or more variables. Clearly identify the independent variables (the variables being changed) and the dependent variables (the variables being measured), as well as the population you are studying. Review and revise your hypothesis as needed.

An example of a research hypothesis in this format is as follows:

“ If [athletes] follow [cold water showers daily], then their [endurance] increases.”

Population: athletes

Independent variable: daily cold water showers

Dependent variable: endurance

You may have understood the characteristics of a good hypothesis . But note that a research hypothesis is not always confirmed; a researcher should be prepared to accept or reject the hypothesis based on the study findings.

Research hypothesis checklist

Following from above, here is a 10-point checklist for a good research hypothesis :

Testable: A research hypothesis should be able to be tested via experimentation or observation.
Specific: A research hypothesis should clearly state the relationship between the variables being studied.
Based on prior research: A research hypothesis should be based on existing knowledge and previous research in the field.
Falsifiable: A research hypothesis should be able to be disproven through testing.
Clear and concise: A research hypothesis should be stated in a clear and concise manner.
Logical: A research hypothesis should be logical and consistent with current understanding of the subject.
Relevant: A research hypothesis should be relevant to the research question and objectives.
Feasible: A research hypothesis should be feasible to test within the scope of the study.
Reflects the population: A research hypothesis should consider the population or sample being studied.
Uncomplicated: A good research hypothesis is written in a way that is easy for the target audience to understand.

By following this research hypothesis checklist , you will be able to create a research hypothesis that is strong, well-constructed, and more likely to yield meaningful results.

Types of research hypothesis

Different types of research hypothesis are used in scientific research:

1. Null hypothesis:

A null hypothesis states that there is no change in the dependent variable due to changes to the independent variable. This means that the results are due to chance and are not significant. A null hypothesis is denoted as H0 and is stated as the opposite of what the alternative hypothesis states.

Example: “ The newly identified virus is not zoonotic .”

2. Alternative hypothesis:

This states that there is a significant difference or relationship between the variables being studied. It is denoted as H1 or Ha and is usually accepted or rejected in favor of the null hypothesis.

Example: “ The newly identified virus is zoonotic .”

3. Directional hypothesis :

This specifies the direction of the relationship or difference between variables; therefore, it tends to use terms like increase, decrease, positive, negative, more, or less.

Example: “ The inclusion of intervention X decreases infant mortality compared to the original treatment .”

4. Non-directional hypothesis:

While it does not predict the exact direction or nature of the relationship between the two variables, a non-directional hypothesis states the existence of a relationship or difference between variables but not the direction, nature, or magnitude of the relationship. A non-directional hypothesis may be used when there is no underlying theory or when findings contradict previous research.

Example, “ Cats and dogs differ in the amount of affection they express .”

5. Simple hypothesis :

A simple hypothesis only predicts the relationship between one independent and another independent variable.

Example: “ Applying sunscreen every day slows skin aging .”

6 . Complex hypothesis :

A complex hypothesis states the relationship or difference between two or more independent and dependent variables.

Example: “ Applying sunscreen every day slows skin aging, reduces sun burn, and reduces the chances of skin cancer .” (Here, the three dependent variables are slowing skin aging, reducing sun burn, and reducing the chances of skin cancer.)

7. Associative hypothesis:

An associative hypothesis states that a change in one variable results in the change of the other variable. The associative hypothesis defines interdependency between variables.

Example: “ There is a positive association between physical activity levels and overall health .”

8 . Causal hypothesis:

A causal hypothesis proposes a cause-and-effect interaction between variables.

Example: “ Long-term alcohol use causes liver damage .”

Note that some of the types of research hypothesis mentioned above might overlap. The types of hypothesis chosen will depend on the research question and the objective of the study.

Research hypothesis examples

Here are some good research hypothesis examples :

“The use of a specific type of therapy will lead to a reduction in symptoms of depression in individuals with a history of major depressive disorder.”

“Providing educational interventions on healthy eating habits will result in weight loss in overweight individuals.”

“Plants that are exposed to certain types of music will grow taller than those that are not exposed to music.”

“The use of the plant growth regulator X will lead to an increase in the number of flowers produced by plants.”

Characteristics that make a research hypothesis weak are unclear variables, unoriginality, being too general or too vague, and being untestable. A weak hypothesis leads to weak research and improper methods.

Some bad research hypothesis examples (and the reasons why they are “bad”) are as follows:

“This study will show that treatment X is better than any other treatment . ” (This statement is not testable, too broad, and does not consider other treatments that may be effective.)

“This study will prove that this type of therapy is effective for all mental disorders . ” (This statement is too broad and not testable as mental disorders are complex and different disorders may respond differently to different types of therapy.)

“Plants can communicate with each other through telepathy . ” (This statement is not testable and lacks a scientific basis.)

Importance of testable hypothesis

If a research hypothesis is not testable, the results will not prove or disprove anything meaningful. The conclusions will be vague at best. A testable hypothesis helps a researcher focus on the study outcome and understand the implication of the question and the different variables involved. A testable hypothesis helps a researcher make precise predictions based on prior research.

To be considered testable, there must be a way to prove that the hypothesis is true or false; further, the results of the hypothesis must be reproducible.

Frequently Asked Questions (FAQs) on research hypothesis

1. What is the difference between research question and research hypothesis ?

A research question defines the problem and helps outline the study objective(s). It is an open-ended statement that is exploratory or probing in nature. Therefore, it does not make predictions or assumptions. It helps a researcher identify what information to collect. A research hypothesis , however, is a specific, testable prediction about the relationship between variables. Accordingly, it guides the study design and data analysis approach.

2. When to reject null hypothesis ?

A null hypothesis should be rejected when the evidence from a statistical test shows that it is unlikely to be true. This happens when the test statistic (e.g., p -value) is less than the defined significance level (e.g., 0.05). Rejecting the null hypothesis does not necessarily mean that the alternative hypothesis is true; it simply means that the evidence found is not compatible with the null hypothesis.

3. How can I be sure my hypothesis is testable?

A testable hypothesis should be specific and measurable, and it should state a clear relationship between variables that can be tested with data. To ensure that your hypothesis is testable, consider the following:

Clearly define the key variables in your hypothesis. You should be able to measure and manipulate these variables in a way that allows you to test the hypothesis.
The hypothesis should predict a specific outcome or relationship between variables that can be measured or quantified.
You should be able to collect the necessary data within the constraints of your study.
It should be possible for other researchers to replicate your study, using the same methods and variables.
Your hypothesis should be testable by using appropriate statistical analysis techniques, so you can draw conclusions, and make inferences about the population from the sample data.
The hypothesis should be able to be disproven or rejected through the collection of data.

4. How do I revise my research hypothesis if my data does not support it?

If your data does not support your research hypothesis , you will need to revise it or develop a new one. You should examine your data carefully and identify any patterns or anomalies, re-examine your research question, and/or revisit your theory to look for any alternative explanations for your results. Based on your review of the data, literature, and theories, modify your research hypothesis to better align it with the results you obtained. Use your revised hypothesis to guide your research design and data collection. It is important to remain objective throughout the process.

5. I am performing exploratory research. Do I need to formulate a research hypothesis?

As opposed to “confirmatory” research, where a researcher has some idea about the relationship between the variables under investigation, exploratory research (or hypothesis-generating research) looks into a completely new topic about which limited information is available. Therefore, the researcher will not have any prior hypotheses. In such cases, a researcher will need to develop a post-hoc hypothesis. A post-hoc research hypothesis is generated after these results are known.

6. How is a research hypothesis different from a research question?

A research question is an inquiry about a specific topic or phenomenon, typically expressed as a question. It seeks to explore and understand a particular aspect of the research subject. In contrast, a research hypothesis is a specific statement or prediction that suggests an expected relationship between variables. It is formulated based on existing knowledge or theories and guides the research design and data analysis.

7. Can a research hypothesis change during the research process?

Yes, research hypotheses can change during the research process. As researchers collect and analyze data, new insights and information may emerge that require modification or refinement of the initial hypotheses. This can be due to unexpected findings, limitations in the original hypotheses, or the need to explore additional dimensions of the research topic. Flexibility is crucial in research, allowing for adaptation and adjustment of hypotheses to align with the evolving understanding of the subject matter.

8. How many hypotheses should be included in a research study?

The number of research hypotheses in a research study varies depending on the nature and scope of the research. It is not necessary to have multiple hypotheses in every study. Some studies may have only one primary hypothesis, while others may have several related hypotheses. The number of hypotheses should be determined based on the research objectives, research questions, and the complexity of the research topic. It is important to ensure that the hypotheses are focused, testable, and directly related to the research aims.

9. Can research hypotheses be used in qualitative research?

Yes, research hypotheses can be used in qualitative research, although they are more commonly associated with quantitative research. In qualitative research, hypotheses may be formulated as tentative or exploratory statements that guide the investigation. Instead of testing hypotheses through statistical analysis, qualitative researchers may use the hypotheses to guide data collection and analysis, seeking to uncover patterns, themes, or relationships within the qualitative data. The emphasis in qualitative research is often on generating insights and understanding rather than confirming or rejecting specific research hypotheses through statistical testing.

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