Frequency = frequency/total number. Frequency is the numerical value of an actual situation, that is, the frequency of a certain situation under human operation. Frequency is generally expressed in decimals.

Under the same conditions, n experiments were carried out. In these N experiments, the frequency ratio of event A is m, and the frequency of event A is m/n. With the frequency (or frequency), we can know the distribution of numbers.

Extended data:

Calculation example

Hydrological phenomenon is a complex natural phenomenon, and its occurrence probability cannot be known, which can only be inferred by counting the occurrence frequency in the measured hydrological data. Due to the limitation of data, there will always be some errors.

The random variable X, which describes hydrological stochastic phenomena, generally belongs to continuous type, so the probability that X is equal to any number X is p{X=x}. Cumulative percentage curve FX (x) ~ x is used to describe the statistical characteristics of hydrological variables in hydrological calculation. If the probability of annual flood peak discharge at Yichang Station of the Yangtze River is greater than or equal to 80000m3/s, p{X≥80000}=FX(80000).

In hydrological calculation, the frequency density function fX(x) of hydrological variables is estimated by statistical analysis based on measured data, and then the cumulative percentage function fX of hydrological variables can be obtained by integrating fX(x).