How to formulate research hypothesis ? Guide for Medical Students

formulating research hypothesis

Hypotheses are single tentative guesses, good hunches – assumed for use in devising theory or planning experiments intended to be given a direct experimental test when possible”. (Eric Rogers, 1966)

A hypothesis is a conjectural statement of the relation between two or more variables”. (Kerlinger, 1956)
A research question is essentially a hypothesis asked in the form of a question
Basically hypothesis is a statement that is suggested by knowledge or observation but has not, yet, been proved or disproved.” (Macleod Clark J and Hockey L 1981)

In simple small words

Hypothesis is

An educated guess
A tentative point of view
A proposition not yet tested
A preliminary explaination
A preliminary Postulate


The hypothesis is a clear statement of what is intended to be investigated.
It should be specified before research is conducted and openly stated in reporting the results.

This allows to:
Ø Identify the research objectives
Ø Identify the key abstract concepts involved in the research
Ø Identify its relationship to both the problem statement and the literature review

A problem cannot be scientifically solved unless it is reduced to hypothesis form

You must make a prediction/ Statement/ postulation
you must identify at least two variables

Following qualities are needed in your hypothesis:

It should have an elucidating power
It should strive to have an acceptable explaination or accounting of a fact
It must be falsifiable simply: It must be capable of being refuted based on the results of the study
It must be formulated in simple, understandable terms
It should correspond with existing knowledge
In general, a hypothesis needs to be unambiguous, specific, quantifiable, testable and generalizable.

1. A Hypothesis must be conceptually clear
- concepts should be clearly defined
- the definitions should be commonly accepted
- the definitions should be easily communicable

2. The hypothesis should have empirical reference
- Variables in the hypothesis should be empirical realities
- If they are not it would not be possible to make the observation and ultimately the test

3. The Hypothesis must be specific
- Place, situation and operation

4. A hypothesis should be related to available techniques of research
- Either the techniques are already available or
- The researcher should be in a position to develop suitable techniques

5. The hypothesis should be related to a body of theory
- Hypothesis has to be supported by theoretical argumentation
- It should depend on the existing body of knowledge


1. Based on their formulation
Null Hypotheses and Alternate Hypotheses

2. Based on direction
Directional and Non-directional Hypothesis

3. Based on their derivation
Inductive and Deductive Hypotheses
But for all practical purposes we all need to know about the first one

Null Hypotheses (Ho) and Alternate Hypotheses (H1) (The HO AND THE HI)

Null hypothesis always predicts that
No differences between the groups being studied e.g., experimental (drinking)  vs. control group (Non drinking) , No difference in these two groups when incidence of Driving accidents studied among them
No relationship between the variables being studied (eg. Drinking and Driving dont result in accidents)
By contrast, the alternate hypothesis always predicts that there will be a difference between the groups being studied (or a relationship between the variables being studied)

In fact in medical research, Frequently “alternative” is actual desired conclusion of the researcher!
( All we want is to establish that the Alternative hypothesis is true and that can be done by rejecting the null hypothesis)

In above eg,  we want to reject that there is no association between drinking and driving accidents and hence we want to prove that there is in fact a relation. For this we conduct the study in two groups.

Formulate the H0 and H1
Collect data (Observation).
Apply statistical test, and
prove or disprove the null hypothesis.

Remember we dont do it, the other way. Meaning we dont reject or accept the alternative hypothesis.
How strong is that relation depends on statistical parameters like p value.

Drug trial on a new drug

H0: there is no difference between the two drugs on average
H1: the new drug is better than the current drug, on average.

Ho relates to the statement being tested
H1 relates to the statement to be accepted if the null is rejected

The final conclusion - (Always in terms of Ho)

Accept H0 = No difference between old and new drug
Reject H1 = Difference between Old and new exist and is a fact

Lets simplify this

Based on how it's derived, Hypothesis can ALSO be classified as

Inductive and Deductive Hypotheses

Inductive reasoning is the more common way that scientists conduct experiments. Scientists have an idea of something to study more in depth. Then they go and collect data through experiments, observations, or surveys. With all of the data in hand, they analyze it to draw out conclusions.
classified in terms of how they were derived:

Inductive hypothesis - a generalization based on observation

Inductive hypothesis

Deductive Hypotheses on pre-existing theory to start with

Deductive Hypotheses


Forming the hypotheses which will be tested, is one of the steps in the planning the research study

A hypothesis is formulated once,
The problem/point of proving (or disproving) has been identified and
The literature study has been conducted for the same (The researcher is totally aware of the theoretical and empirical background of concerned topic)

The Initial Idea: is the starting point
Often vague or general, it requires refining before research hypotheses can be generated

Refinement of the initial idea is based on
(1) A search of relevant research literature
(2) Initial observations made regarding the topic of study

Then initial idea is narrowed into a statement of the problem

In simple words, Ideas lead to
library research
Statement of problem
Problem statements will become research hypotheses


Identify area of interest to be researched 
Exclusive breast feeding and pneumonia

Identify a research question – more narrow and specific : 
Does exclusive breast feeding reduces occurrence of pneumonia ?”

Define the variables 
Pneumonia in infancy, community acquired pneumonia

Formulate the hypothesis by making it a conditional statement
Exclusively breast feeding reduces the occurrence of community acquired pneumonia in infancy

Refine it by writing a formalized hypothesis like 
"If exclusive breast feeding reduces occurrence of CAP the exclusively breast fed babies has a lesser chance to develop pneumonia in infancy”
This type of "if-then" hypothesis is considered the most useful.

Verify that a treatment or exposure is included in the experiment – exclusive breast feeding

Prepare for an outcome measure
Rate of exclusively breast fed babies developing pneumonia

Understand your control group 
Non exclusive breast fed babies
Remember: - Hypothesis can be adjusted/refined/changed as more information is gathered but before the actual examination/experiment is carried out