# hypothesis test

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## hypothesis

[hi-poth´ĕ-sis]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*(

*H*

_{0}) that the effect under investigation does not exist and the

*alternative hypothesis*(

*H*

_{1}) that some specified effect does exist, based on the observed value of a

*test statistic*whose sampling distribution is completely determined by

*H*

_{0}. The decision is made to reject

*H*

_{0}and by implication to accept

*H*

_{1}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

*H*

_{0}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

*H*

_{1}.

## hypothesis test

A statistical procedure to determine the probability (p) that the observed result of a test or trial could have been obtained if the NULL HYPOTHESIS were true.## test

1. an examination or trial.

2. a significant chemical reaction.

3. a reagent. See also under specific names of tests.

*cis*-*trans*testused in microbial genetics to determine whether two mutations that have the phenotypic effect, in a haploid cell or a cell with single phage infection, are located in the same gene or in different genes; the test depends on the independent behavior of two alleles of a gene in a diploid cell or in a cell infected with two phages carrying different alleles.

**critical titer test**

the titer of a test at which the patient is judged to have reacted positively to the test.

**diazo test**

a group of tests for bilirubin conjugates in urine and therefore suitable for the detection of biliary and hepatic disease. Based on the combination of bilirubin with a stable diazonium compound.

**exact test**

a statistical test based on the exact distribution of the data under the null hypothesis, rather than on a normal approximation.

**hypothesis test**

the method by which a hypothesis is judged.

**sodium sulfanilate clearance test**

see sulfanilate.

**test station**

set up by the government or a cooperative organization for the purpose of testing individual livestock provided by farmers for productivity in terms of egg production, milk yield, weight gain. The feeding and measurement are under the control of the station.

**statistical test**

used to decide between two hypotheses.

**surrogate test**

an indirect test, e.g. milk cell count.

**tolerance test**

1. an exercise test to determine the efficiency of the circulation.

2. determines the body's ability to metabolize a substance or to endure administration of a drug, e.g. insulin tolerance test.

**triglyceride absorption test**

see fat absorption test.

**urine concentration test**

see water deprivation test.

**V-test**

a dexamethasone suppression test followed by an ACTH response test; the name refers to the change in plasma cortisone levels, first depressed then elevated, which if plotted on a graph would form a V.

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