A per cent mille or pcm is one one-thousandth of a percent. It can be thought of as a "milli-percent". It is commonly used in
epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and Risk factor (epidemiology), determinants of health and disease conditions in a defined population, and application of this knowledge to prevent dise ...
, and in
nuclear reactor
A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
engineering as a unit of reactivity.
Epidemiology
Statistics
Statistics (from German language, German: ', "description of a State (polity), state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a s ...
of
crime rates,
mortality and
disease prevalence in a population are often given in
Nuclear Reactivity
In nuclear reactor engineering, a per cent mille is equal to one-thousandth of a percent of the
reactivity, denoted by Greek lowercase letter
rho
Rho (; uppercase Ρ, lowercase ρ or ; or ) is the seventeenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 100. It is derived from Phoenician alphabet, Phoenician letter resh . Its uppercase form uses the same ...
. Reactivity is a dimensionless unit representing a departure from
criticality, calculated by:
:
where k
eff denotes the
effective multiplication factor for the reaction. Therefore, one pcm is equal to:
:
This unit is commonly used in the operation of
light-water reactor sites because reactivity values tend to be small, so measuring in pcm allows reactivity to be expressed using whole numbers.
Related units
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Percentage point
A percentage point or percent point is the unit (measurement), unit for the difference (mathematics), arithmetic difference between two percentages. For example, moving up from 40 percent to 44 percent is an increase of 4 percentage points (altho ...
difference of 1 part in 100
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Percentage
In mathematics, a percentage () is a number or ratio expressed as a fraction (mathematics), fraction of 100. It is often Denotation, denoted using the ''percent sign'' (%), although the abbreviations ''pct.'', ''pct'', and sometimes ''pc'' are ...
(%) 1 part in 100
*
Per mille
The phrase per mille () indicates parts per thousand. The associated symbol is , similar to a per cent sign but with an extra zero in the division (mathematics), divisor.
Major dictionaries do not agree on the spelling, giving other options o ...
(‰) 1 part in 1,000
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Basis point
A basis point (often abbreviated as bp, often pronounced as "bip" or "beep") is one hundredth of 1 percentage point. Changes of interest rates are often stated in basis points. For example, if an existing interest rate of 10 percent is increased ...
(bp) difference of 1 part in 10,000
*
Permyriad (‱) 1 part in 10,000
*
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction.
Since these fractions are quantity-per-quantity meas ...
including parts-per million, parts-per billion etc
See also
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InHour (another unit of reactivity)
*
Dollar (reactivity)
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Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction.
Since these fractions are quantity-per-quantity meas ...
*
Per-unit system
*
Percent point function
Notes
Units of measurement
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