18 Units of Measure

Most units of measure are abbreviated when used with numerals or in a virgule construction. Certain units of measure should be spelled out at first mention, with the abbreviated form in parentheses. Thereafter, the abbreviated form should be used in text. (See , Abbreviations, Units of Measure.) ...Less

The SI is based on 7 fundamental units (base units) that refer to 7 basic quantities of measurement (see the tabulation below). These units form the structure from which other measurement quantities are composed.Although not included among the 7 base units, the liter is widely used in the SI as a fundamental measure of capacity or volume. The liter is the recommended unit for measurement of volume for liquids and gases, whereas the cubic meter is the SI unit of volume for solids. Although the kelvin is the SI unit for thermodynamic temperature, the degree Celsius is used with the ...Less

A unit of measure that follows a number at the beginning of a sentence, title, or subtitle should not be abbreviated, even though the same unit of measure is abbreviated if it appears elsewhere in the same sentence. (See , Numbers and Percentages, Spelling Out Numbers, Beginning a Sentence, Title, Subtitle, or Heading; and , Numbers and Percentages, Spelling Out Numbers, Common Fractions.) ...Less

The SI unit names are written lowercase (eg, kilogram) when spelled out, except for Celsius (as in “degrees Celsius”), which is capitalized. Abbreviations or symbols for SI units also are written lowercase, with the following exceptions: ▪ Abbreviations derived from a proper name should be capitalized (eg, N for newton, K for kelvin, A for ampere), although nonabbreviated SI unit names derived from a proper name are not capitalized (eg, newtons, amperes).▪ An uppercase letter L is used as the abbreviation for liter to avoid confusion with the lowercase letter l and the number 1.▪ Certain SI prefixes are capitalized ...Less

In the United States, most physicians and other health care professionals use conventional units for most commonly encountered clinical measurements (eg, blood pressure), and most clinical laboratories report many laboratory values by means of conventional units. To serve these readers, but also to serve the needs of readers in countries where SI units are used, JAMA and the Archives Journals have adopted an approach for reporting units of measure that includes a combination of SI units and conventional units.Measurements of length, area, volume, and mass are reported by means of metric units rather than English units (Table ). In less ...Less

Amounts of money in US, Canadian, and British currency are expressed as a decimal number or whole number preceded by the symbol for the unit of measure for the currency.The cost-effectiveness analysis suggested a $7000 difference between the 2 treatment strategies.In JAMA and the Archives Journals, for amounts reported in non-US currency, the current exchange rate should be used to calculate the amount in US dollars, and that amount should be shown in parentheses. A list of some international currencies and their symbols is provided in Table . Online currency converter programs also are available., The baseline amount for the ...Less

The decimal format is recommended for numbers used with units of measure. Numerical values less than 1 require placement of 0 before the decimal marker.However, certain statistical values, such as α levels and P values, should be reported without the use of 0 before the decimal marker. (See , Numbers and Percentages, Forms of Numbers, Decimals; and , Study Design and Statistics, Glossary of Statistical Terms.)The sample size was based on detecting a 10% difference in the primary outcome measure, using a 2-sided α level of .05. Statistical significance was defined as P < .01.Fractions should not be used with SI units.Mixed ...Less

Other SI measurement quantities are referred to as derived units and are expressed as products or quotients of the 7 base units. Certain derived SI units have special names and symbols and may be used in algebraic relationships to express other derived units. See the following tabulation. ...Less

Drug doses are expressed in conventional metric mass units (eg, milligrams or milligrams per kilogram), rather than in molar SI units. Moreover, certain drugs (such as insulin or heparin) may be prepared as mixtures and have no specific molecular weight, thereby precluding their expression in mass units. Although other drug dose units such as drops (for ophthalmologic preparations), grains (for aspirin), and various apothecary system measurements (eg, teaspoonfuls, ounces, and drams) may be encountered clinically, these units generally are not used. Also, the units for drug doses are often different from the units used to measure drug concentrations, such as ...Less

The calorie is the unit of measure often used in chemistry and biochemistry for reporting heat energy. A value of 1 calorie is the amount of energy (heat) required to raise the temperature of 1 g of pure water by 1°C. The joule is the preferred SI unit for energy, and calories and kilocalories may be converted to joules (J) and kilojoules (kJ) by using the following formulas: 1 calorie = 4.186 J 1 kilocalorie = 4.186 kJJAMA and the Archives Journals prefer to report heat energy in calories or kilocalories.Formerly a distinction was made between this “small calorie” (with ...Less