| correlation coefficient | A measure of association that indicates the degree to which two variables have a linear relationship; this coefficient, represented by the letter r, can vary between +1 and -1; when r = +1, there is a perfect positive linear relationship in which one variable relates directly with the other; when r = -1, there is a perfect negative linear relationship between the variables. (05 Mar 2000) |
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| rank-difference correlation | The relationship between paired series of measurements, each ranked according to magnitude, which yields a coefficient known as rho; the value of rho varies from zero (no relationship) to +1.00 (perfect relationship). (05 Mar 2000) |
| correlation | <statistics> most generally, the degree to which one phenomenon or random variable is associated with or can be predicted from another. In statistics, correlation usually refers to the degree to which a linear predictive relationship exists between random variables, as measured by a correlation coefficient. Correlation may be positive, i.e., both variables increase or decrease together or negative or inverse, i.e., one variable increases when the other decreases. (18 Nov 1997) |
| product-moment correlation | A statistical procedure which yields the correlation coefficient referred to as r (-1.00 to +1.00) and involves the actual values, rather than the ranks (rank order) of the measurements. (05 Mar 2000) |
| Rahn-Otis sample | An approximation of alveolar gas continuously provided by a simple device that admits just the latter part of each expiration. (05 Mar 2000) |
| random sample | A group selected randomly, solely by chance. (12 Dec 1998) |
| Haldane-Priestley sample | <physiology> An approximation of alveolar gas obtained from the end of a sudden maximal expiration into a Haldane tube. (05 Mar 2000) |
| probability sample | Each individual in the sample has a known, generally equal, chance of being selected. (05 Mar 2000) |
| sample | 1. A specimen of a whole entity small enough to involve no threat or damage to the whole; an aliquot. 2. A selected subset of a population; a sample may be random or nonrandom (haphazard); representative or nonrepresentative. Origin: M.E. Ensample, fr. L. Exemplum, example (05 Mar 2000) |
| sample, random | A group selected randomly, solely by chance. (12 Dec 1998) |
| sample size | The number of units (persons, animals, patients, specified circumstances, etc.) in a population to be studied. The sample size should be big enough to have a high likelihood of detecting a true difference between two groups. (12 Dec 1998) |
| stratified sample | A subset of a total population, defined by some objective criterion such as age or occupation, is sampled. (05 Mar 2000) |
| end-tidal sample | A sample of the last gas expired in a normal expiration, ideally consisting only of alveolar gas. (05 Mar 2000) |
| absorption coefficient | <physics> Measures the degree of wave absorption defined as the fraction of wave energy lost as the wave travels a unit distance. See: absorption. (15 Jan 1998) |
| activity coefficient | <chemistry> The factor by which the value of a concentration of a solute must be multiplied to determine its true thermodynamic activity. (06 May 1997) |