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Some commonly used symbols are as follows: The following symbols are usually reserved for specific values For a list of additional symbols that are used in statistics, see , Study Design and Statistics, Statistical Symbols and Abbreviations. The following are examples of these commonly used mathematical expressions: Online journals should ensure that any symbols rendered in HTML are compatible across most commonly used browser platforms. An image should be used if incompatibility is possible. The World Wide Web consortium (http://www.w3.org) provides updated information about browser compatibility issues. | Less

It is essential to mark carefully each character, letter, and symbol that may be mistaken for another form (eg, x, X, χ2, ×2, 2x, x2). The following examples show correct markup for complex relations between elements of equations: In expressions that involve both superscripts and subscripts, the subscript is usually aligned directly under the superscript. In online publication, this alignment can generally be created only by using an image. | Less

Simple formulas may remain within the text of the manuscript if they can be set on the line: The pulmonary vascular resistance index (PVRI) was calculated as follows: PVRI = (MPAP − PCWP)/CI, where MPAP indicates mean pulmonary artery pressure; PCWP, pulmonary capillary wedge pressure; and CI, cardiac index. Long or complicated formulas should be centered on a separate line. In either case, symbols and signs should be marked in detail. Such formulas may be handled either as copy or as prepared art, depending on the availability of special characters and use of software for equation preparation. For online publications, formulas that require more Less

The product of 2 or more terms, including units of measure, is conventionally indicated by a raised multiplication dot (·) (eg, 7 kg · m2) or by 2 or more characters closed up (eg, y = mx + b). However, in scientific notation the times sign (×) is used (eg, 3 × 10−10 cm) (see , Units of Measure, Use of Numerals With Units, Multiplication of Numbers). An asterisk should not be used to represent multiplication, despite its use in this role in computer programs. Note: However, there may be occasions on which the asterisk may be used to provide the reader Less

Use of radicals may sometimes be avoided by substituting a fractional exponent: (a2−b2)1/2instead of a2−b2. As with unstacking fractions, if clarity is sacrificed by making the equation fit within the text, it is preferable to set it off. For example, E = 1.96 {[P (1 − P)]/m}1/2 fits within the text, but the centered E=1.96P(1−P)m might be more easily understood. | Less

The term log is an abbreviation of logarithm. A system of logarithms may be based on any number, although logarithmic systems based on the numbers 10, 2, and the irrational number e are most common. The base should be subscripted and follow the word log. In the following examples, note that logarithms are always computed from exponents of the number that forms their basis.log10 1000 = 3 (because 1000 = 103) log2 8 = 3 (because 8 = 23) Logarithms based on e (which is approximately 2.71) are called natural logarithms and are often represented as ln.ln 2.71 = 1 Less

Long formulas may be given in 2 or more lines by breaking them at operation signs outside brackets or parentheses and keeping the indention the same whenever possible (some formulas may be too long to permit indention). If lines begin with an operation sign, they should be lined up with the first character to the right of the relation sign in the line above.Y=[(a1+b1)/(a2−b2)]+[(σ1+σ2)/(σ2−σ1)]+[(s1+s2)/(t1+t2)] However, if a formula loses comprehensibility by being unstacked and broken up, and/or if it fits the width of the column, it is preferable to leave it stacked.Percent Excess Weight Loss =(Baseline Weight − Ideal Weight)−(Follow-up − Ideal Weight)Baseline Weight − Ideal Weight×100 | Less

A negative exponent denotes the reciprocal of the expression, as illustrated in these examples: x−n= 1/xn A−1 = 1/A B−2 = 1/B2 A negative exponent may simplify some expressions within running text: A(x+y)2 may also be written  as  A(x+y)-2 or A/(x+y)2 | Less

Punctuation after a set-off equation is helpful and often clarifies the meaning. Display equations are often preceded by punctuation. In the linear quadratic equation model, the survival probability for cells receiving a j increment of radiation, Dj, is as follows: S = exp(−αDj − βDj), where α and β are the parameters of the linear quadratic equation model. Do not use periods after a set-off equation if the equation is preceded by a period. | Less