P value: definition of p value by Medical dictionary

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 p value

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Related to p value: confidence interval

value

 [val´u]

1. a measure of worth or efficiency.

2. a quantitative measurement of the activity, concentration, or some other quality of something.

3. an operational belief; an ideal, custom, institution of a society toward which the members of the group have an affective regard; any object or quality desirable as a means or as an end in itself. In exchange theory, the benefits received through an exchange minus the price paid in return.

biological value the quality of a protein expressed on a scale of 1 to 100; the higher the number the better the quality.

cultural v's prevailing and persistent guides influencing the thinking and action of members of a cultural group. Values direct one's perceptions of others and serve as the basis for a person's opinions. Individuals belonging to groups with different cultural values may clash on health and illness behavior.

normal v's the range in concentration of specific substances found in normal healthy tissues, secretions, and so on.

P value (p value) the probability of obtaining by chance a result at least as extreme as that observed, even when the null hypothesis is true and no real difference exists; when P < 0.05 the sample results are usually deemed significant at a statistically important level and the null hypothesis rejected. See also Type I error.

reference v's a set of values of a quantity measured in the clinical laboratory that characterize a specified population in a defined state of health. The values obtained from a statistical sample are used to establish a reference interval that covers 95 per cent of the values of the healthy general population or of specific subpopulations differing in age and sex. These concepts were originally and are still widely referred to as “normal values” and the “normal range,” but the use of these terms is now discouraged because of their implication that values falling outside of the reference interval are “abnormal” or “unhealthy,” which has led to much confusion. It must be remembered that, by definition, 5 per cent of healthy individuals fall outside of the reference interval.

Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

P value

(in research) the statistical probability of the occurrence of a given finding by chance alone in comparison with the known distribution of possible findings, considering the kinds of data, the technique of analysis, and the number of observations. The P value may be noted as a decimal: P <.01 means that the likelihood that the phenomena tested occurred by chance alone is less than 1%. The lower the P value, the less likely the finding would occur by chance alone.

Mosby's Medical Dictionary, 9th edition. © 2009, Elsevier.

p value

The probability that a finding has occurred randomly rather than as a result of a treatment or other intervention. In a research study that compares a treated group of patients with a control group exposed only to a placebo, investigators may find that the treated population experienced benefits or suffered more side effects than the controls. Was the observed effect real, or did it occur by chance? The p value of the study helps researchers tell the difference. A p value of 0.5 suggests that there is a 50-50 chance that the findings of the study are significant. A p value of 0.05 (the value customarily used to suggest that research results are statistically significant) means that there is a 5% chance that the results of the study occurred by chance alone. The lower the value, the greater the degree of confidence in the findings: a p value of 0.01, for example, creates more confidence than a p value of 0.05.

Medical Dictionary, © 2009 Farlex and Partners

significance 

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 p value, which leads us to reject or accept the null hypothesis H_o (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.

Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann