σ2: variance, degree of dispersion of data.
The distribution of continuous random variables with two parameters μ and σ2. The first parameter μ is the mean of a random variable that obeys normal distribution, and the second parameter σ 2 is the variance of this random variable, so the normal distribution is recorded as N(μ, σ 2).
μ is the position parameter of normal distribution, which describes the centralized trend position of normal distribution. The law of probability is that the probability of taking a value close to μ is high, and the probability of taking a value far from μ is low. Normal distribution takes X=μ as the symmetry axis, and the left and right sides are completely symmetrical. The expectation, mean, median and mode of normal distribution are all the same, which are all equal to μ.
σ describes the dispersion degree of normal distribution data. The larger σ is, the more dispersed the data distribution is, and the smaller σ is, the more concentrated the data distribution is. Also known as the shape parameter of normal distribution, the greater σ, the flatter the curve; Conversely, the smaller σ is, the thinner the curve is.
Extended data:
Properties of normal distribution curve;
1, when x < μ, the curve rises; When x > μ, the curve decreases.
When the curve extends infinitely to the left and right sides, the X axis is an asymptote.
2. The normal curve is symmetrical about the straight line x=μ.
3. The larger σ is, the flatter the normal curve is; The smaller σ is, the steeper the normal curve is.
4. The area under the normal curve and on the X axis is 1.
3σ principle:
P(μ-σ