<P> The complement of the standard normal CDF, Q (x) = 1 − Φ (x) (\ displaystyle Q (x) = 1 - \ Phi (x)), is often called the Q - function, especially in engineering texts . It gives the probability that the value of a standard normal random variable X (\ displaystyle X) will exceed x (\ displaystyle x): P (X> x) (\ displaystyle P (X> x)). Other definitions of the Q (\ displaystyle Q) - function, all of which are simple transformations of Φ (\ displaystyle \ Phi), are also used occasionally . </P> <P> The graph of the standard normal CDF Φ (\ displaystyle \ Phi) has 2-fold rotational symmetry around the point (0, 1 / 2); that is, Φ (− x) = 1 − Φ (x) (\ displaystyle \ Phi (- x) = 1 - \ Phi (x)). Its antiderivative (indefinite integral) is </P> <Dl> <Dd> ∫ Φ (x) d x = x Φ (x) + φ (x). (\ displaystyle \ int \ Phi (x) \, (\ rm (d)) x = x \ Phi (x) + \ varphi (x).) </Dd> </Dl> <Dd> ∫ Φ (x) d x = x Φ (x) + φ (x). (\ displaystyle \ int \ Phi (x) \, (\ rm (d)) x = x \ Phi (x) + \ varphi (x).) </Dd>

What does it mean for a distribution to be normal