| E(X) | expected value of the random variable X |
|---|---|
| MRF | Markov random field; medical record file; melanocyte-[stimulating hormone]-releasing factor; mesence... |
| RAM | random-access memory; rapid alternating movements; rectus abdominis muscle; rectus abdominis myocuta... |
| RBS | random blood sugar; Roberts syndrome; Rutherford backscattering |
| RDB | random double-blind [trial] |
| random mating equilibrium | <genetics> In a population containing the genotypes of AA, aa, and Aa, the frequency of AA will be p2, the frequency of aa will be q2, and the frequency of Aa will be 2 pq at equilibrium, where p is the frequency of A and q is the frequency of a. By the Hardy-Weinberg law, a ramdonly-mating population will eventually reach these frequencies and be at this equilibrium as long as there are no selection pressures on the population. (09 Oct 1997) |
|---|---|
| random mechanism | A scheme for substrate binding and product release for a multisubstrate enzyme; for a two-substrate two-product enzyme with this mechanism, either substrate can bind first and, after the reaction has taken place, either product can be the first to dissociate from the enzyme. Brain hexokinase has a random mechanism. More complex random mechanisms exist for enzymes having more than two substrates. (05 Mar 2000) |
| random pattern flap | A flap in which the pedicle blood supply is derived randomly from the network of vessels in the area, rather than from a single longitudinal artery as in an axial pattern flap. (05 Mar 2000) |
| random sample | A group selected randomly, solely by chance. (12 Dec 1998) |
| random sampling | A selection of elements by a formal randomizing device for purposes of inference about a population of inference from that population in such a way that the probability of each possible outcome may be precisely specified in advance; the inferences are necessarily stochastic. (05 Mar 2000) |
| random variable | A variable that may assume a set of values, each with fixed probabilities or probability densities (its distribution), in such a way that the total probability assigned to the distribution is unity; the random variable may be discrete, continuous, or mixed discrete-continuous. (05 Mar 2000) |
| random walk | <cell biology> A description of the path followed by a cell or particle when there is no bias in movement. The direction of movement at any instant is not influenced by the direction of travel in the preceding period. If changes of direction are very frequent, then the displacement will be small, unless the speed is very great and the object will appear to vibrate on the spot. Although the behaviour of moving cells in a uniform environment can be described as a random walk in the long term, this is not true in the short term because of persistence. (18 Nov 1997) |
| random waves | Wave's in the electroencephalogram which occur paroxysmally and asynchronously. (05 Mar 2000) |
| mixed discrete-continuous random variable | <statistics> A random variable that may assume some values with probabilities and others with probability densities. For example, in a 35-year-old man with familial polyposis of the colon, the distribution of time until malignant disease occurs consists of a probability that he already has cancer (which would be assigned the waiting time 0), a probability density of developing it in the future and a probability that he will die of some other cause before he develops cancer. (05 Mar 2000) |
| continuous random variable | Continuous variable that may randomly assume any value in its domain but any particular value has no probability of occurring, only a probability density. (05 Mar 2000) |
| sample, random | A group selected randomly, solely by chance. (12 Dec 1998) |
| pure random drift | That which has random components only with an average value of zero and no systematic effects. Brownian movement in a still container shows pure random drift but in the Mississippi shows a steady downstream tendency. (05 Mar 2000) |
| discrete random variable | A random variable that may assume a countable number of values, each with a probability strictly greater than zero. (05 Mar 2000) |
| ordered on-random off mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with this mechanism, the individuals have to bind to the enzyme in a distinct order; however, once the products are formed they may dissociate from the enzyme in either order. It has been suggested that pyruvate kinase has such a mechanism. The random on-ordered off mechanism is simply the reverse of this mechanism. (05 Mar 2000) |