Non Directional Hypothesis Statements

Aims and Hypotheses

Saul McLeod published 2014


An aim identifies the purpose of the investigation. It is a straightforward expression of what the researcher is trying to find out from conducting an investigation.

The aim typically involves the word “investigate” or “investigation”.

For example:

  • Milgram (1963) investigated how far people would go in obeying an instruction to harm another person.

  • Bowlby (1944) investigated the long-term effects of maternal deprivation.

Types of Hypotheses

A hypothesis (plural hypotheses) is a precise, testable statement of what the researchers predict will be the outcome of the study.

This usually involves proposing a possible relationship between two variables: the independent variable (what the researcher changes) and the dependant variable (what the research measures).

In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).

Briefly, the hypotheses can be expressed in the following ways:

  • The null hypothesis states that there is no relationship between the two variables being studied (one variable does not affect the other). It states results are due to chance and are not significant in terms of supporting the idea being investigated.

  • The alternative hypothesis states that there is a relationship between the two variables being studied (one variable has an effect on the other). It states that the results are not due to chance and that they are significant in terms of supporting the theory being investigated.

In order to write the experimental and null hypotheses for an investigation, you need to identify the key variables in the study. A variable is anything that can change or be changed, i.e. anything which can vary. Examples of variables are intelligence, gender, memory, ability, time etc.

A good hypothesis is short and clear should include the operationalized variables being investigated.

For Example

Let’s consider a hypothesis that many teachers might subscribe to: that students work better on Monday morning than they do on a Friday afternoon (IV=Day, DV=Standard of work).

Now, if we decide to study this by giving the same group of students a lesson on a Monday morning and on a Friday afternoon and then measuring their immediate recall on the material covered in each session we would end up with the following:

  • The experimental hypothesis states that students will recall significantly more information on a Monday morning than on a Friday afternoon.

  • The null hypothesis states that these will be no significant difference in the amount recalled on a Monday morning compared to a Friday afternoon. Any difference will be due to chance or confounding factors.

The null hypothesis is, therefore, the opposite of the experimental hypothesis in that it states that there will be no change in behavior.

At this point you might be asking why we seem so interested in the null hypothesis. Surely the alternative (or experimental) hypothesis is more important?

Well, yes it is. However, we can never 100% prove the alternative hypothesis. What we do instead is see if we can disprove, or reject, the null hypothesis.

If we can’t reject the null hypothesis, this doesn’t really mean that our alternative hypothesis is correct – but it does provide support for the alternative / experimental hypothesis.

One tailed or two tailed Hypothesis?

A one-tailed directional hypothesis predicts the nature of the effect of the independent variable on the dependent variable.

    • E.g.: Adults will correctly recall more words than children.

A two-tailed non-directional hypothesis predicts that the independent variable will have an effect on the dependent variable, but the direction of the effect is not specified.

    • E.g.: There will be a difference in how many numbers are correctly recalled by children and adults.

How to reference this article:

McLeod, S. A. (2014). Aims and hypotheses. Retrieved from



a supposition that appears to explain a group of phenomena and is advanced as a bases for further investigation.

alternative hypothesis the hypothesis that is formulated as an opposite to the null hypothesis in a statistical test.

complex hypothesis a prediction of the relationship between two or more independent variables and two or more dependent variables.

directional hypothesis a statement of the specific nature (direction) of the relationship between two or more variables.

Lyon hypothesis a hypothesis about development of X chromosomes in the embryo; see lyon hypothesis.

Monro-Kellie hypothesis [mun-ro´ kel´e] an explanation of the maintenance of intracranial pressure: The skull is viewed as a closed container housing brain tissue, blood, and cerebrospinal fluid; a change in any of these three components will affect the other two. If the volume added to the cranial vault is equal to the volume displaced, the intracranial volume will not change.

nondirectional hypothesis a statement that a relationship exists between two variables, without predicting the exact nature (direction) of the relationship.

null hypothesis the hyothesis that the effect, relationship, or other manifestation of variables and data under investigation does not exist; an example would be the hypothesis that there is no difference between experimental and control groups in a clinical trial.

hypothesis test the abstract procedure that is the theoretical basis of most statistical tests. A hypothesis test decides between two hypotheses, the null hypothesis (H0) that the effect under investigation does not exist and the alternative hypothesis (H1) that some specified effect does exist, based on the observed value of a test statistic whose sampling distribution is completely determined by H0. The decision is made to reject H0 and by implication to accept H1 when the test statistic falls within a given set of values called the critical region. This region is so determined that the probability of rejecting H0 when it is in fact true (a so-called Type I error, the reporting as significant results that are only the result of random variation and not a real effect), is set at a specified level (symbol α). When this level is set before the data are collected, usually at 0.05 or 0.01, it is called the significance level or α level. It is now more common to report the smallest α at which the null hypothesis can be rejected; this is called the significance probability or P value. The ability of the test to accept a true alternative (and thus to detect a real effect when it exists) is termed the power of the test. Note that no statistical test actually tests the H1.



A conjecture advanced for heuristic purposes, cast in a form that is amenable to confirmation or refutation by conducting of definable experiments and the critical assembly of empiric data; not to be confused with assumption, postulation, or unfocused speculation.
See also: postulate, theory.

[G. foundation, assumption fr. hypotithenai, to lay down]


/hy·poth·e·sis/ (hi-poth´ĕ-sis) a supposition that appears to explain a group of phenomena and is advanced as a basis for further investigation.

alternative hypothesis  one that is compared with the null hypothesis in a statistical test.

biogenic amine hypothesis  the hypothesis that depression is associated with deficiency of biogenic amines, especially norepinephrine, at functionally important receptor sites in the brain and that elation is associated with excess of such amines.

jelly roll hypothesis  a theory explaining the formation of nerve myelin, which states that it consists of several layers of the plasma membrane of a Schwann cell wrapped spirally around the axon in a jelly roll fashion.

lattice hypothesis  a theory of the nature of the antigen-antibody reaction which postulates reaction between multivalent antigen and divalent antibody to give an antigen-antibody complex of a lattice-like structure.

Lyon hypothesis  the random and fixed inactivation (in the form of sex chromatin) of one X chromosome in mammalian cells at an early stage of embryogenesis, leading to mosaicism of paternal and maternal X chromosomes in the female.

null hypothesis  the particular one under investigation, which frequently asserts a lack of effect or of difference.

one gene–one polypeptide chain hypothesis  a gene is the DNA sequence that codes for the production of one polypeptide chain. Antibodies are an exception; separate genes for variable and constant regions are rearranged to code for a single polypeptide.

response-to-injury hypothesis  one explaining atherogenesis as initiating with some injury to the endothelial cells lining the artery walls, which causes endothelial dysfunction and leads to abnormal cellular interactions and initiation and progression of atherogenesis.

sliding filament hypothesis  the stretching of individual muscle fibers raises the number of tension-developing bridges between the sliding contractile protein elements (actin and myosin) and thus augments the force of the next muscle contraction.

Starling's hypothesis  the direction and rate of fluid transfer between blood plasma in the capillary and fluid in the tissue spaces depend on the hydrostatic pressure on each side of the capillary wall, on the osmotic pressure of protein in plasma and in tissue fluid, and on the properties of the capillary walls as a filtering membrane.

wobble hypothesis  one describing how a specific transfer RNA (tRNA) molecule can translate different codons in a messenger RNA (mRNA) template. It states that the third base of the tRNA anticodon does not have to pair with a complementary codon (as do the first two) but can form base pairs with any of several related codons.



1. A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.

2. Something taken to be true for the purpose of argument or investigation; an assumption.

3. The antecedent of a conditional statement.



Etymology: Gk, groundwork


Epidemiology A supposition, arrived at from observation or reflection, that leads to refutable predictions; a conjecture cast in a form that will allow it to be tested and refuted


, pl. hypotheses (hī-poth'ĕ-sis, -sēz)

A conjecture cast in a form that is amenable to confirmation or refutation by experiment and the assembly of data; not to be confused with assumption, postulation, or unfocused speculation.
See also: postulate, theory

[G. foundation, assumption fr. hypotithenai, to lay down]


A tentative proposition used as a basis for reasoning or experimental research, by means of which it may be rejected or incorporated into accepted knowledge. See NULL HYPOTHESIS.


a proposition assumed on the basis of observation which might account for or explain something which is not fully understood. see SCIENTIFIC METHOD.


a provisional or tentative theory, not yet supported by a significant amount of corroborative evidence.


theory unsupported by substantiated facts or data that would prove or deny its truth; null and alternate hypotheses are compared by statistical tests, and probability (that an observed effect is true or not) is determined by statistical evaluation of P -value
  • alternative hypothesis; research hypothesis assumption that any difference noted (within a variable under different conditions) has occurred as the direct result of the observed or imposed changes

  • null hypothesis assumption that any difference noted (within a variable under different conditions) has occurred by chance


n an experimentally testable proposal given as the basis for additional examination.


In statistics, an indication that the results of an investigation on a population (e.g. patients) differ from those of another population (e.g. general) by an amount that could not happen by chance alone. This is evaluated by establishing a significance level, that is the probability, called pvalue, which leads us to reject or accept the null hypothesis Ho (there is no significant difference between two populations and the difference is attributed to chance) and accept or reject the alternative hypothesis H1 that there is a statistically significant difference between two populations. A p value p < 0.05 is often considered significant, but the lower this figure, the stronger the evidence. See randomized controlled trial.


, pl. hypotheses (hī-poth'ĕ-sis, -sēz)

A conjecture advanced for heuristic purposes, cast in a form that is amenable to confirmation or refutation by conducting of definable experiments and the critical assembly of empiric data.
See also: theory

[G. foundation, assumption fr. hypotithenai, to lay down]


a supposition that appears to explain a group of phenomena and is assumed as a basis of reasoning and experimentation.

hypothesis testing

a standard practice using statistical methods, usually analytical observational studies, to differentiate between two hypotheses. For example, the user assumes that vaccination against a particular disease reduces the prevalence of the disease, then tests that hypothesis.

hypothesis testing sampling

sampling of material or data for the purpose of testing a hypothesis.

0 thoughts on “Non Directional Hypothesis Statements

Leave a Reply

Your email address will not be published. Required fields are marked *