(1) population and sample
① In statistics, the whole research object is called population. ② Each research object is called an individual. ③ The total number of individuals in the population is called the total capacity.
④ In order to study the related properties of the population, we generally randomly select a part from the population: x 1, x2, ..., xx research, which we call samples. The number of individuals is called sample size.
(2) Simple random sampling, also known as pure random sampling. That is, as a whole, it does not go through any grouping, classification, queuing, etc. , completely with.
Machine-based measurement unit extraction. The characteristics are: the probability of each sample unit being extracted is the same (the probability is equal), and each unit of the sample is completely independent, and there is no certain correlation and exclusion between them. Simple random sampling is the basis of other sampling forms. This method is usually only used when the difference between the whole units is small and the number is small.
(3) Common methods of simple random sampling:
1 draw lots; ② Random number table; ③ Computer simulation; ③ Direct extraction with statistical software.
In the sample size design of simple random sampling, the main considerations are: ① population variation; ② Allowable error range; ③ Degree of probability assurance.
(4) draw lots:
(1) Number each object in the measurement group; (2) Prepare the lottery tool and implement it;
③ Measure or investigate each individual in the sample.
(5) Random number table method: