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Base rate fallacy
| Glossary of Statistical Terms |
The base rate fallacy consists of failing to take into account prior probabilities (base rates) when computing conditional probabilities from other conditional probabilities. it is related to the prosecutor`s fallacy. for instance, suppose that a test for the presence of some condition has a 1% chance of a false positive result (the test says the condition is present when it is not) and a 1% chance of a false negative result (the test says the condition is absent when the condition is present), so the exam is 99% accurate. what is the chance that an item that tests positive really has the condition? the intuitive answer is 99%, but that is not necessarily true: the correct answer depends on the fraction f of items in the population that have the condition (and on whether the item tested is selected at random from the population). the chance that a randomly selected item tests positive is 0.99×f/(0.99×f + 0.01×(1−f)), which could be much smaller than 99% if f is small. see bayes` rule.
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Conditional, английский
- Условный
- A условный | n 1 усло- вие2; 2 грм. а) условное наклонение (син. ~ mood), б) условная связь (син. ~ conjunction); 3 лог. условное высказывание mood, sentence
- In probabilistic expert systems, a collection of conditional distributions for the same group of variables (referred to as the head) over all of the states of a conditioning set of variables (referred to as the tail). the conditional distribution of height and weight for various mutually exclusive groupings of age and sex would be a conditional, with height and weight as the head variables and age and sex the tail variables. see also: slice.
- A control structure such as an if-statement or case-statement that conditionally executes a block of code
Prosecutor, английский
A trial lawyer representing the government in a criminal case and the interests of the state in civil matters. in criminal cases, the prosecutor has the r
Population, английский
- A definable set of individual units to which the findings from statistical examination of a sample subset are intended to be applied. the population will generally much outnumber the sample. in re-randomisation statistics the process of applying inference
- See stock.
- A collection of units being studied. units can be people, places, objects, epochs, drugs, procedures, or many other things. much of statistics is concerned with estimating numerical properties (parameters) of an entire population from a random sample of units from the population.
- A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age).
- Население; народонаселение; генеральная совокупность (в выборочном наблюдении); популяция (биол)
- Население
- 1. the number of people living in a country or town population statistics show that the birth rate is slowing down. the government has decided to screen the whole population of the area. 2. the number of patients in hospital the hospital population in the area has fallen below 10,000.
- Популяция
- Население; популяция -
- Популяция. в клинических исследованиях совокупность субъектов, обладающих какими-либо одинаковыми признаками (пол, возраст, диагноз).
- Население; популяция
- Any group of individuals, usually of a single species, occupying a given area at the same time; groups of organisms with homologue (same) alleles. p. cycle: changes in the numbers of individuals in a population which repeatedly oscillate between periods of high and low density. p. density: allowing a mathematically precise reflection - pd. • absolute: pd = number of individuals/unit area or volume [1/m2] or [1/m3] • relative: pd allows only a simple comparison (pd <, =, >, ? etc.). p. dynamics: the variations in time and space in the sizes and densities of populations; distribution due to changing food resources - the stability of a population depends upon abiotic factors, intraspecific competition (density dependent), natality, mortality etc. p. ecology: the study of the variations in time and space in the sizes and densities of populations, and of the factors causing those variations. p. fluctuation: variations over time in the size of a population. p. growth: is zero, when the birth rate equals the death rate (see carrying capacity). nt+1 = nt + r nt, current number of individuals r = (natality + immigration) - (mortality+emigration) r, intrinsic rate of growth (see density) p. pyramid: a means of illustrating the age structure of a population diagrammatically, by placing the youngest age class at the base and stacking successive age classes above it. p. regulation : a tendency in a population for some factor to cause density to increase when it is low and to decrease nt, momentary number of individuals when it is high. n0, number of individuals at start
- Generally, a collection of individuals with common characteristics. in statistics, a potentially infinite collection of independent (->independence) units that include all units of a specified type with attention paid only to the agggregate (->aggregation) property of the collection. a sample of data drawn from this population is a subset of the units constituting this population and scientific generalizations from such samples are limited by the size of the population originally specified (->model, ->representation).
- The process of scanning content to compile and maintain an index.
- Fish of the same species inhabiting a specified geographic area.
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Placebo effect, английский
- The belief or knowledge that one is being treated can itself have an effect that confounds with the real effect of the treatment. subjects given a placebo as a pain-killer report statistically significant reductions in pain in randomized experiments that compare them with subjects who receive no treatment at all. this very real psychological effect of a placebo, which has no direct biochemical effect, is called the placebo effect. administering a placebo to the control group is thus important in experiments with human subjects; this is the essence of a blind experiment.
- The apparently beneficial effect of telling someone that he or she is having a treatment, even if this is not true, caused by the hope that the treatment will be effective
- Плацебо-эффект. эффект в результате применения плацебо.
Sample mean, английский
The arithmetic mean of a random sample from a population. it is a statistic commonly used to estimate the population mean. suppose there are n data, {x1, x2, … , xn}. the sample mean is (x1 + x2 + … + xn)/n. the expected value of the sample mean is the population mean. for sampling with replacement, the se of the sample mean is the population standard deviation, divided by the square-root of the sample size. for sampling without replacement, the se of the sample mean is the finite-population correction ((n−n)/(n−1))½ times the se of the sample mean for sampling with replacement, with n the size of the population and n the size of the sample.
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