Types of Hypotheses in scientific research (and examples)

There are different types of hypotheses in scientific research. From null, general or theoretical hypotheses, to complementary, alternative or working hypotheses.

• Related article: "The 15 types of research (and their characteristics)"

What is a hypothesis?

But, What exactly is a hypothesis and what is it for? The hypotheses specify the possible characteristics and results that may exist between certain variables that are going to be studied.

Through the scientific method, an investigator should try to verify the validity of his initial (or main) hypothesis. This is what is usually called a working hypothesis. At other times, the researcher has several complementary, or alternative hypotheses in mind.

If we examine these working hypotheses and alternatives, we find three subtypes: attributive, causal and associative hypotheses. General or theoretical hypotheses serve to establish a relationship (negative or positive) between the variables, while the working hypotheses and alternatives are those that effectively quantify said relationship.

On the other hand, the null hypothesis is the one that reflects that there is no appreciable link between the variables studied. In the case in which it cannot be verified that the working hypotheses and the alternative hypotheses are valid, the null hypothesis is admitted as correct.

Although these are considered the most common types of hypotheses, there are also relative and conditional hypotheses. In this article we will discover all the types of hypotheses, and how they are used in scientific investigations.

What are hypotheses for?

Any scientific study must be started taking into account one or more hypotheses that is intended to confirm or refute.

A hypothesis is nothing more than a conjecture that may or may not be confirmed by scientific study. In other words, hypotheses are scientists' way of posing the problem, establishing possible relationships between variables.

Types of hypotheses used in a scientific study

There are several criteria that can be followed when classifying the types of hypotheses used in science. We will meet them below.

1. Null hypothesis

The null hypothesis refers to the fact that there is no relationship between the variables that have been investigated. It is also called the "non-relationship hypothesis", but it should not be confused with a negative or inverse relationship. Simply, the variables studied do not seem to follow any specific pattern.

The null hypothesis is accepted if the scientific study results in the working and alternative hypotheses not being observed.

Example

"There is no relationship between people's sexual orientation and their purchasing power."

2. General or theoretical hypotheses

The general or theoretical hypotheses are those that scientists establish prior to the study and conceptually, without quantifying the variables. Generally, the theoretical hypothesis arises from processes of generalization through certain preliminary observations about the phenomenon they wish to study.

Example

"The higher the level of studies, the higher the salary." There are several subtypes within the theoretical hypotheses. Difference hypotheses, for example, specify that there is a difference between two variables, but do not measure its intensity or magnitude. Example: "In the faculty of Psychology there are a greater number of female students than male students".

3. Work hypothesis

The working hypothesis is the one that serves to try to demonstrate a concrete relationship between variables through a scientific study. These hypotheses are verified or refuted by means of the scientific method, which is why they are sometimes also known as “operational hypotheses”. Generally, working hypotheses are born from deduction: from certain general principles, the researcher assumes certain characteristics of a particular case. The working hypotheses have several subtypes: associative, attributive and causal.

3.1. Associative

The associative hypothesis specifies a relationship between two variables. In this case, if we know the value of the first variable, we can predict the value of the second.

Example

"There are twice as many enrolled in the first year of high school than in the second year of high school."

3.2. Attributive

The attributive hypothesis is the one used to describe the events that occur between the variables. It is used to explain and describe real and measurable phenomena. This type of hypothesis only contains one variable.

Example

"Most homeless people are between the ages of 50 and 64."

3.3. Causal

The causal hypothesis establishes a relationship between two variables. When one of the two variables increases or decreases, the other undergoes an increase or decrease. Therefore, the causal hypothesis establishes a cause-effect relationship between the variables studied. To identify a causal hypothesis, a cause-effect link, or statistical (or probabilistic) relationship, must be established. It is also possible to verify this relationship through the refutation of alternative explanations. These hypotheses follow the premise: "If X, then Y".

Example

"If a player trains an additional hour each day, his hitting percentage increases by 10%."

4. Alternative hypotheses

Alternative hypotheses attempt to provide an answer to the same question as working hypotheses. However, and as can be deduced from its name, the alternative hypothesis explores different relationships and explanations. In this way, it is possible to investigate different hypotheses during the course of the same scientific study. This type of hypothesis can also be subdivided into attributive, associative and causal.

More types of hypotheses used in science

There are other types of hypotheses that are not so common, but are also used in different types of research. They are as follows.

5. Relative hypotheses

The relative hypotheses give evidence of the influence of two or more variables on another variable.

Example

“The effect of the decline in GDP per capita on the number of people who have plans for private pensions is less than the effect of the drop in public spending on the malnutrition rate childish".

• Variable 1: decrease in GDP
• Variable 2: drop in public spending
• Dependent variable: number of people who have a private pension plan

6. Conditional hypotheses

Conditional hypotheses serve to indicate that a variable depends on the value of two others. It is a type of hypothesis very similar to the causal ones, but in this case there are two “cause” variables and only one “effect” variable.

Example

"If the player receives a yellow card and is also warned by the fourth official, he must be excluded from the game for 5 minutes."

• Cause 1: receive a yellow card
• Cause 2: being noticed
• Effect: being excluded from the game for 5 minutes. As we can see, for the "effect" variable to occur, it is not only necessary that one of the two "cause" variables be fulfilled, but both.

Other kinds of hypotheses

The types of hypotheses that we have explained are those most commonly used in scientific and academic research. However, they can also be classified based on other parameters.

7. Probabilistic hypotheses

This type of hypothesis indicates that there is a probable relationship between two variables. That is, the relationship is true in most of the cases studied.

Example

"If the student does not spend 10 hours a day reading, (probably) he will not pass the course."

8. Deterministic hypotheses

Deterministic hypotheses indicate relationships between variables that always hold true, without exception.

Example

"If a player does not wear cleated boots, he will not be able to play the game."

Bibliographic references:

• Hernández, R., Fernández, C., and Baptista, M.P. (2010) Research Methodology (5th Ed.). Mexico: McGraw Hill Education
• Salkind, N.J. (1999). Research Methods. Mexico: Prentice Hall.
• Santisteban, C. and Alvarado, J.M. (2001). Psychometric Models. Madrid: UNED