Research Writing

Types of hypothesis in research/Characteristics/Importance


The hypothesis is the attempt to explain some phenomenon or problem that can be corroborated through observation or experimentation. Scientists need to propose hypotheses as possible explanations for the problem they want to solve.

“It is what someone thinks of the reality they are investigating and that because they are not certain about it, they should prove it.”

The hypothesis is the proposition that a certain event will cause a hitherto unknown effect. Both cause and effect must be related in some logical way, and arise from previous antecedents.

Not all investigations require the statement or formulation of hypotheses. When an investigation does not seek to prove something, it does not need a hypothesis. For example, if the study is about the physical characteristics of adolescents from a certain school, it is a descriptive investigation, without the need for hypotheses.

Characteristics of the hypotheses

  • They must be testable: a hypothesis must be demonstrable through observations and / or experiments. For example, research hypothesizing that increased salt intake in men between the ages of 40 and 60 causes an increase in blood pressure can be demonstrated. Instead, to say that the black hole in the Milky Way increases the solar temperature is difficult to verify with current instruments and technology.
  • It can be falsifiable : this means that it can be rejected through experiments. A hypothesis can be true or false; It is through experimentation and data collection and analysis that we can conclude on the veracity of it.
  • They must be specific : general hypotheses, such as “eating eggs causes heart disease”, are not valid because they are very broad. In this case, it is not specified what type of eggs, the quantity or the frequency; The relationship between egg consumption and how the disease occurs is not expressed either. A better hypothesis would be “people between the ages of 60 and 70 who consume more chicken eggs per week will have a greater increase in blood cholesterol levels.”
  • They must be objective : hypotheses must be focused on the aspects of reality to be investigated; our perceptions should not be part of them. For example, a researcher who is very fond of coffee may be tempted to hypothesize that coffee improves the well-being of humanity, which is neither objective nor specific.

Types of hypotheses

There are different types of hypotheses according to various points of view. According to the objective, we find descriptive and explanatory hypotheses.

Descriptive hypotheses

This type of hypothesis seeks to describe the correlation between phenomena and not the reasons why they occur. Examples:

  1. The proportion of women smokers has increased in the last decade.
  2. Smokers are at higher risk for lung problems.
  3. People who consume large amounts of salt have hypertension problems.

Explanatory hypothesis

When we are interested in discovering why the events occur and the explanation of them, we propose explanatory hypotheses. Examples:

  1. Higher levels of stress in women lead to addictive behaviors like smoking.
  2. The compounds in cigarettes cause the lung cells to malfunction.
  3. Sodium chloride causes the muscle cells in the arteries to contract.

Null hypothesis and alternative hypothesis

The terms null hypothesis and alternative hypothesis are applied in statistical analyzes when you want to compare parameters between populations. In this case, the null hypothesis refers to the fact that there is no difference between the populations with respect to the parameter evaluated, and the alternative hypothesis establishes that there are differences.

It is good to clarify that the null hypothesis does not mean that it is wrong.

How to make a hypothesis

A hypothesis is a conjecture that can be tested and / or examined. As such it should be expressed as a statement or proposition in the simplest possible way. Some prefer to express the hypotheses in the format ” if A is, then B happens “.

When we have a hypothesis we must know “what produces what”, that is, what is the cause and what is the effect . The hypothesis assumes that the fact X has the effect Y . These facts are what we know as variables .

For example, in the hypothesis “people between 60 and 70 years who consume more chicken eggs per week will have a greater increase in blood cholesterol levels”, the variables are egg consumption and blood cholesterol level.

In all hypotheses, the relationship between cause and effect must be clearly established and at least two facts must be related.

There may be more than one hypothesis for a problem. For example, if you want to investigate the reason for the greater height of adolescents in a country, you can hypothesize about the quality and / or quantity of food, the genetics of parents or the physical activity of young people.

Difficulties in formulating hypotheses

  • Lack of knowledge of the theoretical framework : hypotheses arise after establishing the theoretical framework, not before.
  • Lack of knowledge of the techniques available to test hypotheses : if we do not know how to prove that a hypothesis is true or false, we will hardly be able to state it correctly.

Importance of the hypothesis

  • Orientation and guidance of the investigation : the hypothesis proposes the direction that the investigation should follow.
  • Relationship between the facts : the hypothesis presents the first sketch of how the facts that are the subject of the investigation may be related and why they occur.
  • Link between theory and reality : the hypothesis establishes the connection between what we see in reality and its theoretical explanation.
  • Stimulation of logic and creativity : many hypotheses have been the fruit of the creativity of scientists who introduce new ideas based on logical aspects.

Examples of hypotheses

Here are several examples of scientific hypotheses.

Sugary drinks and cancer

The increase in the consumption of sugary drinks in recent decades and the impact of these on metabolic diseases is well known. In a population study in France, it was suggested that this increase could also be related to oncological diseases. The hypothesis most in line with this research would be:

The increased consumption of sugary drinks increases the risk of suffering from some form of cancer.

In this case, the hypothesis is descriptive because it did not seek to demonstrate the cause by which sugar could promote cancer. In this study, 101 257 participants older than 18 years were selected and classified according to their consumption of beverages with sugar greater than 5%. After 5 years, the data on sugar consumption and the appearance of some type of cancer were analyzed.

Popeye and spinach

For those who do not know the Popeye the sailor cartoon , this was a sailor whose particular characteristic was to become stronger when he ate spinach. Certainly, spinach has compounds that improve physical activity in these animals in experimental rats and mice.

A group of researchers in Germany made the following hypothesis:

The compound in spinach that works in animals also improves physical activity in humans.

The hypothesis was tested by supplementing 22 athletes with the compound in question for ten weeks, and they were compared with 24 other athletes who acted as controls. After ten weeks, an increase in muscle mass and an improvement in physical performance were observed, which showed that the hypothesis was correct.

The super glue of snails

We have seen how snails can move on rough, inclined surfaces and even parallel to the ground without falling. This is thanks to the mucus they produce at their base. Researchers in South Korea and the US established the following hypothesis:

Creating a material with the properties of snail mucus will work as a strong, reversible adhesive.

They then invented a methacrylate-based polymeric hydrogel system that acts as a reversible super adhesive.

Hypothesis of importance to humanity

There are probably millions of scientific hypotheses since ancient times the human being has tried to give explanations to the phenomena he observed. Here are some examples of scientific hypotheses and how they were corroborated.

The endosymbiotic hypothesis

Lynn Sagan proposed in 1966 that eukaryotic cells originated from endosymbiosis between photosynthetic and respiratory prokaryotes in a predominantly aerobic environment. Thus, an aerobic prokaryote (protomitochondria) entered the cytoplasm of a heterotrophic anaerobic microorganism.

The corroboration of this hypothesis is based on the particular characteristics of mitochondria and chloroplasts, organelles of eukaryotic cells that have their own DNA.

Tectonic plates

In 1912 the German scientist Alfred Wegener (1880-1930) proposed the concept of continent plate motion. Wegener suggested that millions of years ago the current continents were united into one great and single continent (Pangea), which then cracked apart, each landmass moving apart like the continents we know today.

The bases of this hypothesis were in the coastlines of America that correspond to the coasts of Europe and Africa and in the similar fossils found between these continents. The proof that this hypothesis was correct was demonstrated in the 1960s.

ZIKA virus and microcephaly

Microcephaly is a neurological condition where a baby’s brain does not fully develop, causing the head to appear smaller than normal. In Brazil, more than 8,000 cases were reported between November 2015 and June 2016, representing an alarming increase in this problem.

Around the same time, Zika virus infections also increased. This virus belongs to the same family as the yellow fever virus ( Flaviviridae ) and is transmitted to humans by mosquitoes. Of people infected with the Zika virus, between 20 and 25% have symptoms similar to those of the common cold or flu.

The initial hypothesis suggested that the fetuses of pregnant women infected with the Zika virus may have an increased risk of microcephaly. The results of a case-control study in 2016 showed that 13 of 32 newborns with microcephaly had evidence of virus infection, compared to 62 control newborns who were free of infection, demonstrating the association between Zika and microcephaly .

The Riemann hypothesis

Prime numbers have the property that they cannot be expressed as the product of two smaller numbers. When these prime numbers appear among the natural numbers is difficult to determine. However, the German mathematician G, FB Riemann (1826-1866) proposed an equation, called the Riemann Zeta function, that approximates the frequency of prime numbers.

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