Sampling survey to the total area of the forest of Heshun county in Shanxi province in year 2000
- Calculate the total optimal sample size n according to the known accuracy requirement
- Calculate the sample size nh of each layer h according to the proportion distribution /optimal distribution design of the sample size;
- Randomly extract nh samples from layer h respectively with computer pseudo-random number;
- According to the sampling sites, estimate the population mean, then multiply 2,697,460, the result is the estimated total area ( unit m2）, and estimate the sampling accuracy.
Sample size according to the optimal distribution design:
- Total optimal sample size:
- Sample size of each layer:
- Estimate the mean of the knowledge layer according to 159 sampling sites, from this, estimate the total area and the sampling accuracy :
The total optimal sample size is 142 in fact
The sampling size after extending 10% is 159
If the user knows correlation coefficient r of each knowledge level,then in the formulais
.
；
Population size 
of each layer
；
Each layer variance 
；
Each layer cost 
；
Layer mean 
；
Layer weight 
；
Population mean 
；
Variance 
;
Area weight
of each layer of each reporting unit
。