18 Units of Measure

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

Arabic numerals are used for quantities with units of measure (see , Numbers and Percentages, Use of Numerals). By SI convention, it is preferable to use only numbers between 0.1 and 1000 and to use the appropriate prefix for expressing quantities. For example, 0.003 mL is expressed as 3 μL; 15 000 g is expressed as 15 kg.Some clinical measurements are expressed in quantities and units that may have numbers outside this preferred range. For such values, the use of scientific notation is acceptable.20 000 000 A may be expressed as 20 million amperes or as 2 × 107 AReported ...Less

An index generally refers to a quantity derived from a ratio of 2 (or more) measurable quantities and often is used to compare individuals with each other or with normal values. Except for products or quotients representing specific derived SI units of measure (see also , Expressing Unit Names and Symbols, Products and Quotients of Unit Symbols), the ratio of SI units used to create indexes does not represent an SI convention.At first mention in the text, the formula used to calculate the index should be described; thereafter, the numerical value for the index may be given without units attached ...Less

Multiplication of numbers should be indicated by the multiplication sign (×) and may be used to express area (eg, a 15 × 35-cm2 burn), volume (eg, a 5.2 × 3.7 × 6.9-m3 cube), matrixes (eg, 2 × 2 table), magnification (×30 000), or scientific notation (eg, 3.6 × 109/L). ...Less

By SI convention, the decimal point is the only punctuation mark permitted in numerals, and it is used to separate the integer and decimal parts of the number. The SI does not use commas in numbers, in particular because the comma is used in some countries as the decimal sign. Integers (whole numbers) with more than 4 digits are separated into groups of 3 (using a thin space) with respect to the decimal point. Four-digit integers are closed up (without a space). Decimal digits also are grouped in sets of 3 digits beginning at the decimal sign, with the same ...Less