International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

Multilingual Technical Dictionary (MTD)
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Term No.Term Name/Term DescriptionAction
7
Precision
A quality associated with a class of measurements, refers to the way in which repeated observations conform to themselves; and in a somewhat narrower sense to the dispersion of observations......
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27
Observation error
The difference between an observed value of a quantity and a value adapted as representing the ideal or true value of that quantity. Errors of observations are composed of either one or both of two general classes of errors, accidental errors and systematic errors. The algebraic sign of an observation error is determined from the equation : Error =.....
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31
Conversion factor
That factor by which the numerical value made in one system of units must be multiplied to arrive at the numerical value in another system of units......
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32
Fluctuations
1 - A movement up or down between consecutive items of a series of numbers or numerical observations. 2 - The variation of a statistic from sample to sample is known as a `sampling fluctuation`......
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34
Sampling distribution
The distribution of a statistic (or set of statistics) in all possible samples chosen according to a specified sampling scheme......
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55
Partial duration series above a given base
A list of all events, such as, floods, occurring above a selected base, without regard to the number within a given period. In the case of floods, the selected base is usually equal to the lowest annual flood, in order to include at least one flood, each year......
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68
Cumulative distribution curve, Distribution curve, or Ogive
A graphic plot of the cumulative frequencies for a particular class interval and of all lower class intervals below it (or of all upper class intervals above it) against the class interval concerned. See 864......
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69
Cumulative frequency function curve
Cumulative frequencies divided by the total number of observations, gives the relative cumulative frequency distribution and its plotting against the class interval concerned gives the cumulative frequency function curve......
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73
Correlation diagram, or Scatter diagram
The graphical representation presenting a bivariate frequency distribution when both variables are quantitative.
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74
Duration curve
A curve that expresses the relation of all the units of some item (e.g. flow), arranged in order of magnitude as the ordinate, and time (frequently expressed in percentage) as the abscissa; a graphical representation of the number of times given quantities are equalled or exceeded during a certain period of record. The duration curve is the integra.....
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75
Duration-area curve of flows
A curve that shows the area beneath a duration curve and value of the flow, and is, thus an integral of duration with respect to stream flow. When the duration curve is plotted as a percentage of time, the resulting duration area shows the average flow available below a given discharge......
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77
Flow-duration curve
A duration curve of stream flow.
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79
Mass diagram, Mass curve, Flow integrated curve, or Summation curve
A diagram, curve, or graph, plotted with rectangular coordinates, representing a summation (integration) of all preceding quantities up to a point. Each ordinate being equal to the sum of preceding terms in the series, with the corresponding abscissa representing elapsed time, etc. The diagram is used extensively in storage and regulation studies p.....
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83
Correction
A quantity that is applied to an observation or function thereof to diminish or eliminate the effects of errors and obtain an improved value of the observation or function. It is also applied to reduce an observation to some arbitrary standard. The correction corresponding to a given error is of the same magnitude, but of opposite sign......
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91
Density function, or Frequency function
An expression giving the frequency of a variate X as a function of x; or for continuous variates, the frequency in an elemental range dx......
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93
Relative frequency, or Proportional frequency
A frequency expressed as a proportion of the total number of members.
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95
Frequency distribution
1 - An arrangement or distribution of quantities pertaining to a single element in the order of their magnitude. 2 - A specification of the way in which the frequencies of members of a population are distributed according to the values of the variates which they exhibit......
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97
Percentage distribution
A frequency distribution with the total frequency equated to 100 and the individual class frequencies in proportion to that figure......
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99
Dimensional homogeneity
The condition of an equation when the units of length, time, and mass are identical on both sides of the equality sign.
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117
Average deviation, or Mean deviation
A measure of dispersion derived from the average deviation of observations from some central value, such deviations being absolute, i.e. without reference to algebric sign......
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118
Deviation
1 - The difference between a value (x) and a value (a) that depicts deviation. The absolute value of the deviation, i.e. the value taken without regard to sign, is called the `absolute deviation`. 2 - The algebraic difference between the mean of a series of data and an individual member of the series......
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119
Standard deviation
A measure of dispersion of a frequency distribution equal to the square root of the `variance`. It is the square root of the sum of the squares of the deviations from the arithmetic mean, divided by the number of values or events in the series (See 116)......
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121
Dispersion
1 - The degree of scatter shown by observations. It is usually measured as an average deviation about some central value (e.g. mean deviation, standard deviation) or by an order statistic (e.g. quartile deviation, range). 2 - See 1666......
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122
Coefficient of variation
The standard deviation of a distribution divided by the mean, also expressed as a percentage.
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123
Coefficient of variation of a probability distribution
The ratio of the standard deviation to the absolute value of the expectation.
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