The greater the difference and variance between data Xi and mean EX, the greater the fluctuation of data to mean ex; On the contrary, the smaller;

For example: Xi: 1.000 1, 0.9999, 1.0002, 0.9998; D (x) = 2.5× 10 (-8) variance is very small;

Yi: 1, 2, 3,? 4; D(Y)= 1.25？ Large variance;

You can also look at the curve of probability density function, taking normal distribution as an example:

When the density curve is flat, it means that the data is far from the average, the data variance is large and the data fluctuates greatly;

When the density curve is high, narrow and steep, it shows that the data concentration tends to be average, the data variance is small and the data fluctuation is small.