Commonly Used Symbols

>

greater than

≥

greater than or equal to

>>

much greater than

<

less than

≤

less than or equal to

<<

much less than

±

plus or minus (This symbol should not be used to indicate variability around a central tendency (eg, “The control group had a mean [SD] value of 12 [7],” not “The control group had a mean of 12 ± 7.”)

${\displaystyle {\int }_{\text{a}}^{\text{b}}}$

integral from value of a to value of b

${\displaystyle \sum _{a=1}^{30}}$

summation from a = 1 to a = 30

${\displaystyle \prod _{a=1}^{30}}$

product of a = 1 to a = 30

Δ

delta (change, difference between values)

f

function

≠

not equal to

≈

approximately equal to

∼

similar to (reserve for use in geometry and calculus; use words in other cases where “approximately” is meant)

≅

congruent to

≡

defined as

∞

infinity

!

factorial, eg, n! = n(n − 1) (n − 2)… 1

π

pi (approximately 3.1416). Do not confuse with uppercase Π.

e

base of the system of natural logarithms (approximately 2.7183). See 21.4.3, Exponents, Logarithmic Expressions. In statistical equations, however, “e” may also represent the error term in a regression equation.

i

the square root of −1

>10⁵ CFUs/mL

${\displaystyle {\int }_{10}^{13}2xdx}$

24.5 ± 0.5

$F\sim \frac{m_1{m}_2}{r^2}$

L ≈ 2 × 10¹⁰ m

r ! (n − r)!

f(x) = x + Δx

(e^x + e^−x)/2

y = dx/dt

Y = β₁ + β₂ + e

P < .001

kg · m · s⁻²

${\displaystyle \sum _{i=1}^n{a}_i{x}_i}$

$x+\frac{x^2}{2}+\frac{x^3}{3}+\frac{x^4}{4}+\cdots +\frac{x^n}{n}$ (note that in this case the operation sign is indicated on both sides of the ellipses)